Not sure, Jez, if you have already approached your ISP regarding this. If not, have you inspected your ancient socket very closely, using a hammer if necessary? It might have been damaged by the previous owner of your new house and if so it will need replacement as part of your new installation.

And if it was "accidentally" damaged then BT may still charge to replace - believe that has happened before even when the faceplate was actually damaged before the person moved in.

Precisely because of things like the other poster is suggesting

Indeed. A dangerous thing to advise, especially on an open forum.