I made a complaint about this to BT on 9th December. This afternoon I got a telephone call about it. The conversation lasted some time with him trying to persuade me first that I didn't have a second master socket wired as a secondary socket and then to adopt his solution of plugging in a filter into the secondary socket and taking the broadband from there. He just wouldn't have it that since the broadband signal was filtered out by the first master socket a second filter could not restore the missing signal. He was so adamant about it that I am beginning to doubt my understanding of the problem. BT of course are happy to send out an engineer to fix the problem but "there may be a charge" and I am not going to give them a chance to make me pay for their past errors. I never did get round to pointing out that when I upgraded to Infinity the instruction was to remove all the filters from the secondary sockets and throw the filters away.