No, situated in North London 6 miles from the transmitter (Saffron Green Mast).
I'm starting to get the feeling that this is a mains power problem. I think there's an AC adaptor somewhere picking up the radio station and then feeding it through the power wiring.
What confused me though, was that I completely shut down the house power from the master switch on the consumer unit, connected to the master socket test port and still got the rfi, but it wouldn't happen as often as when on the extension wiring. The very fact that it happened at all on the providers wiring with no power connected (using a simple corded telephone - no psu) is what has thrown me and I have been drawing my attention away from the local environment...
I'm running Quiet Line Tests when I can and systematically changing things until I hit on it... It can't hide forever