Originally Posted by Dan B

The "double-socket" will likely be an SSFP (Service Specific Face Plate), which usually has a filter built into it, so you "shouldn't" need to put a filter on that......everything else WILL need a filter on it, though. If you have a Sky box that's plugged into a proprietary socket, you'll need to check if that has a filter built into it aswell, as it "could" be interfering with the broadband sync-signal.