Redirect Failure for iRule

Have you checked the logic in your code? The first block in the if-statement is executed if the host equals testssl.communigator.co.uk, but it only contains the redirect of the root.

The redirect for the /common/ folder is in the else-block, so the host cannot match testssl.communigator.co.uk. However, in your description you indicate that the request you want to redirect does in fact match that host.