diff --git a/.env.example b/.env.example
index 5bb66c3715..54faff4528 100644
--- a/.env.example
+++ b/.env.example
@@ -31,6 +31,7 @@ AWS_SECRET_KEY=👻
 FILE_API_KEY=👻
 FILE_API_KEY_NEXUS=👻
 FILE_API_KEY_BARNET=👻
+FILE_API_KEY_SOUTHWARK=👻
 
 # Editor
 EDITOR_URL_EXT=http://localhost:3000
diff --git a/api.planx.uk/.env.test.example b/api.planx.uk/.env.test.example
index 947deafa0b..e728faab1f 100644
--- a/api.planx.uk/.env.test.example
+++ b/api.planx.uk/.env.test.example
@@ -20,6 +20,7 @@ AWS_SECRET_KEY=👻
 FILE_API_KEY=👻
 FILE_API_KEY_NEXUS=👻
 FILE_API_KEY_BARNET=👻
+FILE_API_KEY_SOUTHWARK=👻
 
 # Editor
 EDITOR_URL_EXT=example.com
diff --git a/api.planx.uk/modules/auth/middleware.ts b/api.planx.uk/modules/auth/middleware.ts
index b280b2b135..b5e66c9e39 100644
--- a/api.planx.uk/modules/auth/middleware.ts
+++ b/api.planx.uk/modules/auth/middleware.ts
@@ -87,7 +87,14 @@ export const useFilePermission: RequestHandler = (req, _res, next): void => {
       req.headers["api-key"] as string,
       process.env.FILE_API_KEY_NEXUS!,
     ) ||
-    isEqual(req.headers["api-key"] as string, process.env.FILE_API_KEY_BARNET!);
+    isEqual(
+      req.headers["api-key"] as string,
+      process.env.FILE_API_KEY_BARNET!,
+    ) ||
+    isEqual(
+      req.headers["api-key"] as string,
+      process.env.FILE_API_KEY_SOUTHWARK!,
+    );
   if (!isAuthenticated) return next({ status: 401, message: "Unauthorised" });
   return next();
 };
diff --git a/doc/how-to/how-to-setup-aws-s3-submissions.md b/doc/how-to/how-to-setup-aws-s3-submissions.md
new file mode 100644
index 0000000000..998f963a72
--- /dev/null
+++ b/doc/how-to/how-to-setup-aws-s3-submissions.md
@@ -0,0 +1,26 @@
+# How to setup AWS S3 submissions
+
+## Context
+
+When building a submission service, the "Send" component offers an option "Upload to AWS S3" which uploads the application data payload to PlanX's private S3 Bucket - which then in turn allows a council to receive a notification via a Power Automate Webhook and run a script to securely retrieve the application JSON file, download any associated user-uploaded files, generate custom documents, and save the application to their local Microsoft SharePoint environment.
+
+There's full documentation on how this method works in the PlanX Service Specification on Notion [here](https://opensystemslab.notion.site/How-you-can-receive-process-PlanX-applications-using-Microsoft-365-tools-like-Power-Automate-13197a4bbd24421eaf7b5021ddd07741?pvs=4).
+
+Once a council has confirmed they're cleared from their IT dept to use this method (eg allowed to receive external webhook requests) & shared a Power Automate Webhook URL, there's a few steps we need to take:
+
+1. Add the council-provided URL to `team_integrations.power_automate_webhook_url` as plain text via the production Hasura console
+
+2. Create 2x tokens for sending secure requests to the Power Automate webhook and add both encrypted values to:
+  - `team_integrations.production_power_automate_api_key` & `team_integrations.staging_power_automate_api_key` via the production Hasura console
+  - See `how-to-generate-a-secret` for how to properly generate tokens and encrypt values
+
+3. Create 2x tokens for downloading files from the PlanX S3 Bucket and add values to:
+  - Root `.env.example` & `.env`, API's `.env.test` & `.env.test.example` as `FILE_API_KEY_{TEAM_SLUG}`
+    - In addition to committing these changes, also manually sync to AWS `pizza-secrets` via `scripts/push-secrets.sh`
+  - Root `docker-compose.yml`
+  - API's `modules/auth/middleware.ts` function `isAuthenticated`
+  - Pulumi's `infrastructure/application/index.ts` list of `apiService` "environment" variables
+    - Run `pulumi config set file-api-key-{team_slug} --stack {stack}` 2x for each staging & production stacks
+  - Encrypt the values using _our_ encrypt scripts (again see `how-to-generate-a-secret`) and add to `team_integrations.production_file_api_key` & `team_integrations.staging_file_api_key` via the production Hasura console. Please note these values are _not_ currently read, but suitable for a potential future refactor (just a bit tricky because file API keys are issued to a mix of _teams_ and _systems_ (eg BOPS & Idox)).
+
+4. Securely share tokens back to council contact via onetimesecret or similar
diff --git a/docker-compose.yml b/docker-compose.yml
index 3a8af48c12..ea9c787219 100644
--- a/docker-compose.yml
+++ b/docker-compose.yml
@@ -126,6 +126,7 @@ services:
       EDITOR_URL_EXT: ${EDITOR_URL_EXT}
       ENCRYPTION_KEY: ${ENCRYPTION_KEY}
       FILE_API_KEY_BARNET: ${FILE_API_KEY_BARNET}
+      FILE_API_KEY_SOUTHWARK: ${FILE_API_KEY_SOUTHWARK}
       FILE_API_KEY_NEXUS: ${FILE_API_KEY_NEXUS}
       FILE_API_KEY: ${FILE_API_KEY}
       GOOGLE_CLIENT_ID: ${GOOGLE_CLIENT_ID}
diff --git a/editor.planx.uk/src/@planx/components/Send/Editor.tsx b/editor.planx.uk/src/@planx/components/Send/Editor.tsx
index 6cad4a9328..37d7e894a9 100644
--- a/editor.planx.uk/src/@planx/components/Send/Editor.tsx
+++ b/editor.planx.uk/src/@planx/components/Send/Editor.tsx
@@ -113,10 +113,10 @@ const SendComponent: React.FC<Props> = (props) => {
       if (
         value === "s3" &&
         newCheckedValues.includes(value) &&
-        !["barnet", "lambeth"].includes(teamSlug)
+        !["barnet", "southwark"].includes(teamSlug)
       ) {
         alert(
-          "AWS S3 uploads are currently being prototyped with Barnet and Lambeth only. Please do not select this option for other councils yet.",
+          "AWS S3 uploads require API tokens and are currently being prototyped with select councils. Reach out on Slack #planx-alternatives-to-integrations before selecting this option please.",
         );
       }
     };
diff --git a/infrastructure/application/Pulumi.production.yaml b/infrastructure/application/Pulumi.production.yaml
index 23f8804851..cef9dd5308 100644
--- a/infrastructure/application/Pulumi.production.yaml
+++ b/infrastructure/application/Pulumi.production.yaml
@@ -12,6 +12,8 @@ config:
     secure: AAABANMl+fVFsRVGXvJV/aLManXO+TldXVDhp5QH6KGWJoG7O9Ket63zIW1iOiinINWJ2I5OizI=
   application:file-api-key-nexus:
     secure: AAABAB2cv4GAf8RqN1hHbRbO68p8o4kLJYWsip9BoPdobrNtQB787M3s+gJnKKl9DfyXRHOXHGc=
+  application:file-api-key-southwark:
+    secure: AAABAL5G2cNl6XIQA0vcP6El4Us7Vk8Cz9JViRon25crc8MC0ix4ox2mE+XawsxYbLRwGfaRIJo=
   application:google-client-id: 987324067365-vpsk3kgeq5n32ihjn760ihf8l7m5rhh8.apps.googleusercontent.com
   application:google-client-secret:
     secure: AAABAN5E+De3A3HtpLVaSNTDwk9Uz4r2d5g8SIRVbNOd2fj3eU+lGJXjVbEAnxezr14hwabbfwW2ptjcFzqkhG7OmQ==
diff --git a/infrastructure/application/Pulumi.staging.yaml b/infrastructure/application/Pulumi.staging.yaml
index 9ffd625e37..a037794324 100644
--- a/infrastructure/application/Pulumi.staging.yaml
+++ b/infrastructure/application/Pulumi.staging.yaml
@@ -13,6 +13,8 @@ config:
     secure: AAABAFpZq81zy3CKFXUgi9oEGIGp7LDVD3TNlYkZD4liX0bxOrmMJYdDpMmyGt4aGARF63nEUmo=
   application:file-api-key-nexus:
     secure: AAABAJFgaBoTWNmZyXDkGRngwU8KpOt6CeBLxGBgBG0JFMsKK7rWT39TsjJ9pL1wZaBoT0YZhCg=
+  application:file-api-key-southwark:
+    secure: AAABAK8LsYKKNgIS4fepW5Sh6+WKxNopxsos51eBttT7O8E8K0HYOswgrIWuYJ0R1eJHDLKRHqQ=
   application:google-client-id: 987324067365-vpsk3kgeq5n32ihjn760ihf8l7m5rhh8.apps.googleusercontent.com
   application:google-client-secret:
     secure: AAABAGQuqQDU4S+vR+cQaFoa6xAeWU9clVaNonQ/dq0R8Dke+o0y7ALOmYMy4fOX4Pa6HiZl85npU/cbwy8HdMYaiA==
diff --git a/infrastructure/application/index.ts b/infrastructure/application/index.ts
index a9bed3ad7c..8fde151cd4 100644
--- a/infrastructure/application/index.ts
+++ b/infrastructure/application/index.ts
@@ -348,6 +348,10 @@ export = async () => {
             name: "FILE_API_KEY_BARNET",
             value: config.requireSecret("file-api-key-barnet"),
           },
+          {
+            name: "FILE_API_KEY_SOUTHWARK",
+            value: config.requireSecret("file-api-key-southwark"),
+          },
           {
             name: "GOOGLE_CLIENT_ID",
             value: config.require("google-client-id"),