Hi fuzzums,
I am sorry to hear about this problem with your line.
I read from your post that you've already checked your telephone sockets. I would recommend also having a look at the link below and see if there is anything there that you haven't tried yet:
http://bt.custhelp.com/cgi-bin/bt.cf...45%2C353%2C374
If you're still having problems after the troubleshooting test the next thing to do is to contact the BT faults team. I'll send you a PM and if you want I can arrange to have your line checked for you.
Once the faults team carries out their preliminary tests they should get a better idea as to where the fault is.
Cheers,
Stephanie
BT Support