diff --git a/README.md b/README.md
index d7e15ee..f1c3499 100644
--- a/README.md
+++ b/README.md
@@ -107,6 +107,43 @@ pkill -f "node server/index.js"
   accounts.
 - `ENABLE_LOG_STREAM` - set to `false` to disable the `/logs` streaming endpoint
   in production and avoid exposing real-time log data if not required.
+- `ALLOWED_SOURCE_DOMAINS` - comma-separated list of additional hostnames that
+  administrators are permitted to use when defining custom feeds. The value is
+  merged with the built-in allow list (which already includes
+  `contracts.mod.uk` for the DSTL portal).
+
+### Allowing additional source domains
+
+If you see a message similar to `Search URL rejected: Host "contracts.mod.uk"
+is not on the allow list` while adding a feed, extend the allow list using the
+`ALLOWED_SOURCE_DOMAINS` environment variable. Example commands:
+
+- **Linux/macOS/Raspberry Pi**
+  ```bash
+  export ALLOWED_SOURCE_DOMAINS="contracts.mod.uk"
+  ```
+- **Windows PowerShell**
+  ```powershell
+  $env:ALLOWED_SOURCE_DOMAINS="contracts.mod.uk"
+  ```
+
+Restart the server after setting the variable so the new domains are loaded.
+Multiple hostnames can be supplied by separating them with commas, for example
+`contracts.mod.uk,example.org`.
+
+For convenience, the helper script below can export the variable and launch the
+server in one step:
+
+```bash
+./scripts/run.sh --allow-domain contracts.mod.uk
+```
+
+To configure a Raspberry Pi in a single command, the setup script forwards the
+same option to the background server:
+
+```bash
+./scripts/rpi_bidfinder.sh --allow-domain contracts.mod.uk 4000
+```
 
 ## Scheduled cron job
 
diff --git a/frontend/help.ejs b/frontend/help.ejs
index 2f7885a..6627c4d 100644
--- a/frontend/help.ejs
+++ b/frontend/help.ejs
@@ -29,7 +29,7 @@
       <li><strong>Parser</strong> &ndash; choose the parser from the dropdown. The default (<code><%= defaultParser %></code>) matches most Contracts Finder feeds.</li>
     </ul>
     <p>Award sources follow the same structure but point at feeds of awarded contracts.</p>
-    <p class="hint">If you see a “URL not permitted” warning, check that both addresses start with <code>https://</code> and that the hostname appears in the allowed list. Administrators can extend the allow list using the <code>ALLOWED_SOURCE_DOMAINS</code> environment variable (comma-separated hostnames).</p>
+    <p class="hint">If you see a “URL not permitted” warning, check that both addresses start with <code>https://</code> and that the hostname appears in the allowed list. DSTL’s <code>contracts.mod.uk</code> domain is pre-approved, but you can extend the list with the <code>ALLOWED_SOURCE_DOMAINS</code> environment variable or by launching the server through <code>./scripts/run.sh --allow-domain example.org</code>.</p>
   </div>
   <div id="parser-reference">
     <h2>Parser Reference</h2>
diff --git a/scripts/rpi_bidfinder.sh b/scripts/rpi_bidfinder.sh
index 6e11b74..9e4d118 100755
--- a/scripts/rpi_bidfinder.sh
+++ b/scripts/rpi_bidfinder.sh
@@ -1,27 +1,82 @@
 #!/bin/bash
 
-# rpi_bidfinder.sh - prepare the project on a Raspberry Pi.
-# Installs Node.js, fetches dependencies, initialises the database and can
-# optionally launch the server. Use the -p or --production flag to skip dev
-# dependencies and supply a port number to start the server immediately.
-# Usage: ./scripts/rpi_bidfinder.sh [-p|--production] [PORT]
+# ---------------------------------------------------------------------------
+# @file rpi_bidfinder.sh
+# @description Automated setup routine tailored for Raspberry Pi deployments.
+#   The script installs Node.js, fetches dependencies, initialises the SQLite
+#   database and optionally launches the Procurement Scraper GUI. Operators can
+#   skip development dependencies, choose a listening port and extend the
+#   allowed domain list so new feeds (such as DSTL) can be registered without
+#   manual environment configuration.
+# @usage ./scripts/rpi_bidfinder.sh [-p|--production] [PORT]
+#        ./scripts/rpi_bidfinder.sh --allow-domain contracts.mod.uk 4000
+# @structure
+#   1. Parse command-line arguments for production mode, port and domain
+#      options.
+#   2. Install prerequisites and project dependencies.
+#   3. Initialise the database and optionally start the server using run.sh.
+# ---------------------------------------------------------------------------
 
 set -e
 
-# Parse command line options for production mode and optional port number. The
-# port argument can be provided in any position as long as it is not preceded
-# by -p or --production.
+# Parse command line options for production mode, port and allow-list domains.
 PROD=0
 PORT=""
+declare -a RUN_ARGS=()
+
+usage() {
+  cat <<'EOF'
+Usage: ./scripts/rpi_bidfinder.sh [options] [PORT]
+
+Options:
+  -p, --production           Install only production dependencies.
+      --allow-domain <HOST>  Forward hostname to run.sh for allow-listing.
+      --allow-domains <LIST> Forward comma-separated hostnames to run.sh.
+  -h, --help                 Display this help message and exit.
+
+Providing a bare number continues to set the server port for backwards
+compatibility. Any allow-domain options are passed to run.sh so the Node.js
+process receives the expanded ALLOWED_SOURCE_DOMAINS variable.
+EOF
+}
+
 while [[ $# -gt 0 ]]; do
   case "$1" in
     -p|--production)
       PROD=1 # toggle to install only production dependencies
       shift
       ;;
+    --allow-domain)
+      if [[ -z "$2" ]]; then
+        echo "Error: --allow-domain requires a hostname." >&2
+        usage
+        exit 1
+      fi
+      RUN_ARGS+=("--allow-domain" "$2")
+      shift 2
+      ;;
+    --allow-domains)
+      if [[ -z "$2" ]]; then
+        echo "Error: --allow-domains requires a comma-separated list." >&2
+        usage
+        exit 1
+      fi
+      RUN_ARGS+=("--allow-domains" "$2")
+      shift 2
+      ;;
+    -h|--help)
+      usage
+      exit 0
+      ;;
     *)
-      PORT="$1" # treat any other argument as the desired port
-      shift
+      if [[ -z "$PORT" && "$1" =~ ^[0-9]+$ ]]; then
+        PORT="$1" # treat any other argument as the desired port
+        shift
+      else
+        echo "Error: Unknown argument '$1'." >&2
+        usage
+        exit 1
+      fi
       ;;
   esac
 done
@@ -53,7 +108,8 @@ npm run init-db # create the SQLite database
 # exports PORT before starting the Node.js server. The server is started in the
 # background so this script exits immediately.
 if [[ -n "$PORT" ]]; then
-  ./scripts/run.sh "$PORT"
+  RUN_ARGS+=("--port" "$PORT")
+  ./scripts/run.sh "${RUN_ARGS[@]}"
 fi
 
 echo "Setup complete."
diff --git a/scripts/run.sh b/scripts/run.sh
index 0874e57..50881e7 100755
--- a/scripts/run.sh
+++ b/scripts/run.sh
@@ -1,18 +1,133 @@
 #!/bin/bash
 
-# run.sh - convenience wrapper to launch the Procurement Scraper GUI server.
-# Usage: ./scripts/run.sh [PORT]
-#
-# Accepts an optional port argument which is exported as the PORT environment
-# variable so the Express application listens on that interface. The server is
-# started in the background to avoid blocking the calling script. Logs continue
-# to be written to logs/app.log by the application's logger.
+# ---------------------------------------------------------------------------
+# @file run.sh
+# @description Utility wrapper that launches the Procurement Scraper GUI
+#   backend with sensible defaults. The script accepts optional arguments for
+#   setting the HTTP port and extending the domain allow list used when
+#   administrators register new feeds via the UI. By exporting the relevant
+#   environment variables before invoking Node.js, the script keeps runtime
+#   configuration in one place and avoids manual shell commands.
+# @usage ./scripts/run.sh [PORT] [--port PORT] [--allow-domain HOST]
+#        ./scripts/run.sh --allow-domains host1,host2
+# @structure
+#   1. Parse CLI arguments (port plus optional allow-list domains).
+#   2. Export environment variables derived from the parsed arguments.
+#   3. Launch the Node.js server in the background while printing guidance for
+#      retrieving logs.
+# ---------------------------------------------------------------------------
 
 set -e
 
-# Respect the first argument as the desired port if present.
-if [ -n "$1" ]; then
-  export PORT="$1"
+# Track requested port and any allow-list domains supplied by the operator.
+PORT_ARG=""
+declare -a ALLOWED_DOMAINS=()
+
+usage() {
+  cat <<'EOF'
+Usage: ./scripts/run.sh [PORT] [options]
+
+Options:
+  -p, --port <PORT>           Explicitly set the server port.
+      --allow-domain <HOST>   Append a hostname to ALLOWED_SOURCE_DOMAINS.
+      --allow-domains <LIST>  Provide a comma-separated list of hostnames.
+  -h, --help                  Show this message and exit.
+
+Supplying a bare number without --port is still supported for backwards
+compatibility. Hostnames are normalised to lower case and may be specified as
+either raw domains or full HTTPS URLs.
+EOF
+}
+
+# Parse arguments, supporting both legacy positional ports and explicit flags.
+while [[ $# -gt 0 ]]; do
+  case "$1" in
+    -p|--port)
+      if [[ -z "$2" ]]; then
+        echo "Error: --port requires a numeric argument." >&2
+        usage
+        exit 1
+      fi
+      PORT_ARG="$2"
+      shift 2
+      ;;
+    --allow-domain)
+      if [[ -z "$2" ]]; then
+        echo "Error: --allow-domain requires a hostname." >&2
+        usage
+        exit 1
+      fi
+      ALLOWED_DOMAINS+=("$2")
+      shift 2
+      ;;
+    --allow-domains)
+      if [[ -z "$2" ]]; then
+        echo "Error: --allow-domains requires a comma-separated list." >&2
+        usage
+        exit 1
+      fi
+      IFS=',' read -ra MULTI <<<"$2"
+      for dom in "${MULTI[@]}"; do
+        ALLOWED_DOMAINS+=("$dom")
+      done
+      shift 2
+      ;;
+    -h|--help)
+      usage
+      exit 0
+      ;;
+    *)
+      if [[ -z "$PORT_ARG" && "$1" =~ ^[0-9]+$ ]]; then
+        PORT_ARG="$1"
+        shift
+      else
+        echo "Error: Unknown argument '$1'." >&2
+        usage
+        exit 1
+      fi
+      ;;
+  esac
+done
+
+if [[ -n "$PORT_ARG" ]]; then
+  export PORT="$PORT_ARG"
+fi
+
+# Merge supplied domains with any existing ALLOWED_SOURCE_DOMAINS definition.
+if [[ ${#ALLOWED_DOMAINS[@]} -gt 0 ]]; then
+  IFS=',' read -ra EXISTING <<<"${ALLOWED_SOURCE_DOMAINS:-}"
+  COMBINED=()
+  for host in "${EXISTING[@]}"; do
+    COMBINED+=("$host")
+  done
+  for host in "${ALLOWED_DOMAINS[@]}"; do
+    COMBINED+=("$host")
+  done
+
+  declare -A SEEN=()
+  DEDUPED=()
+  for host in "${COMBINED[@]}"; do
+    normalised=$(printf '%s' "$host" | tr '[:upper:]' '[:lower:]' | xargs)
+    if [[ -z "$normalised" ]]; then
+      continue
+    fi
+    if [[ "$normalised" == *"://"* ]]; then
+      normalised=${normalised#*://}
+    fi
+    normalised=${normalised%%/*}
+    normalised=${normalised%%:*}
+
+    if [[ -n "$normalised" && -z "${SEEN[$normalised]}" ]]; then
+      SEEN[$normalised]=1
+      DEDUPED+=("$normalised")
+    fi
+  done
+
+  if [[ ${#DEDUPED[@]} -gt 0 ]]; then
+    ALLOWED_SOURCE_DOMAINS=$(IFS=','; echo "${DEDUPED[*]}")
+    export ALLOWED_SOURCE_DOMAINS
+    echo "Allowing additional source domains: $ALLOWED_SOURCE_DOMAINS"
+  fi
 fi
 
 # Start the Node.js backend in the background. Use nohup so the server keeps
diff --git a/server/config.js b/server/config.js
index dbc3245..76941f3 100644
--- a/server/config.js
+++ b/server/config.js
@@ -30,6 +30,66 @@ function parseSelectorList(value, fallback = []) {
   return [...fallback];
 }
 
+/**
+ * Convert environment input into a deduplicated list of domain names. The
+ * helper accepts a string, array or undefined value and always returns lower
+ * case hostnames without protocols, ports or trailing slashes so downstream
+ * comparisons remain consistent. Full URLs are tolerated for operator
+ * convenience and are reduced to their hostname component.
+ *
+ * @param {string|string[]|undefined} value - Domains supplied via environment
+ * @param {string[]} fallback - Default domains to include when none provided
+ * @returns {string[]} normalised hostname list
+ */
+function parseDomainList(value, fallback = []) {
+  const result = [];
+  const seen = new Set();
+
+  /**
+   * Normalise and register a hostname candidate if it has not been seen before.
+   *
+   * @param {string} candidate - Potential hostname or URL to add
+   */
+  function register(candidate) {
+    if (!candidate) return;
+    let host = candidate.trim().toLowerCase();
+    if (!host) return;
+
+    if (host.includes('://')) {
+      try {
+        host = new URL(host).hostname.toLowerCase();
+      } catch {
+        // Ignore values that are not valid URLs; they will be skipped.
+        return;
+      }
+    }
+
+    host = host.replace(/\/$/, '');
+    if (!host) return;
+
+    // Strip any lingering port numbers (e.g. example.com:8080).
+    const portSeparator = host.indexOf(':');
+    if (portSeparator !== -1) {
+      host = host.slice(0, portSeparator);
+    }
+
+    if (!seen.has(host)) {
+      seen.add(host);
+      result.push(host);
+    }
+  }
+
+  fallback.forEach(register);
+
+  if (Array.isArray(value)) {
+    value.forEach(register);
+  } else if (typeof value === 'string' && value.trim()) {
+    value.split(',').forEach(register);
+  }
+
+  return result;
+}
+
 /**
  * Convert an environment string into a positive integer, falling back to a
  * default when parsing fails or the provided value is out of range.
@@ -96,6 +156,16 @@ const defaultNetwork = {
   detailConcurrency: parsePositiveInt(process.env.HTTP_DETAIL_CONCURRENCY, 4)
 };
 
+// Domains explicitly permitted when administrators add custom sources. The
+// default list includes DSTL's contracts portal to prevent validation failures
+// when configuring the DSTL feed. Operators can extend the allow list via the
+// ALLOWED_SOURCE_DOMAINS environment variable.
+const defaultAllowedDomains = ['contracts.mod.uk'];
+const allowedSourceDomains = parseDomainList(
+  process.env.ALLOWED_SOURCE_DOMAINS,
+  defaultAllowedDomains
+);
+
 // Centralised configuration object used throughout the server code. Values can
 // be overridden via environment variables for flexibility in different
 // deployment environments.
@@ -377,6 +447,11 @@ module.exports = {
   // timeouts, retry counts and detail page concurrency.
   network: defaultNetwork,
 
+  // Hostnames that are always permitted when defining custom sources. Values
+  // come from defaults above and can be extended through the
+  // ALLOWED_SOURCE_DOMAINS environment variable.
+  allowedSourceDomains,
+
   // Legacy fields maintained for backwards compatibility. These map to the
   // default source so existing code and tests continue to work.
   scrapeUrl: defaultSource.url,
diff --git a/server/index.js b/server/index.js
index c5c7a92..58877c5 100644
--- a/server/index.js
+++ b/server/index.js
@@ -68,15 +68,10 @@ function normaliseParserKey(parserKey) {
 // statically configured sources but can be extended via the
 // ALLOWED_SOURCE_DOMAINS environment variable.
 const allowedDomains = new Set([
-  ...Object.values(config.sources).map(s => new URL(s.base).hostname),
-  ...Object.values(config.awardSources).map(s => new URL(s.base).hostname)
+  ...Object.values(config.sources).map(s => new URL(s.base).hostname.toLowerCase()),
+  ...Object.values(config.awardSources).map(s => new URL(s.base).hostname.toLowerCase()),
+  ...config.allowedSourceDomains
 ]);
-if (process.env.ALLOWED_SOURCE_DOMAINS) {
-  for (const dom of process.env.ALLOWED_SOURCE_DOMAINS.split(',')) {
-    const trimmed = dom.trim().toLowerCase();
-    if (trimmed) allowedDomains.add(trimmed);
-  }
-}
 
 /**
  * Validate whether a provided URL is permitted based on protocol and hostname.