Even when plugged directly into test socket with no filters, I am getting no dial tone on my telephone.

So you get no dial tone anywhere ? sounds like one of the two wires in your pair is disconnected, enough ADSL is getting down the one wire for it to hang on.

If no dialtone at test socket when ALL broadband hardware is disconnected, then report a voice fault. Clear and simple.

Surely if this is the case, as it is plugged into test socket and still not working properly, it must be on BT's side, rather than that of the internal wiring?

Yes that's what Yarwell was saying. If you get no dial tone at the NTE, with nothing else connected, then you have a good old fashioned line fault. Ring your voice provider and have them arrange that it be fixed.
What do you hear if you ring your landline number from your mobile ?
Straight to answerphone, then a loop fault, just rings, then it's one leg disconnected.

Just keeps ringing, so I guess one leg is disconnected in that case. Thanks for your help.