I had a lot of interferance on my landline Phone 1 Month ago, including beeping.
Called BT, and now all is well.
Has the exchange at Penge (se20) converted to 21cn?

Assuming your exchange is Sydenham, it certainly possible - planned for Q4, 2008.

http://www.samknows.com/broadband/exchange/LSSYD

Thanks for the link. Having said my phone service is now as it should be and has been for a few weeks, it beeped whilst I was not using it. What a coincidence.