Given the agony of Virgin helpline on a PAYG mobile at my expense, is this a standard item I can order elsewhere ? - any "BT socket to RJ11 adaptor" ?
The adapter is a standard item which you can get from your preferred online supplier for just a few pounds. The VM forum team often arrange for one to be dropped of by a passing technician if required. An ordinary modern conventional phone should also work. A very old phone (approx. 15+ years) might have problems.
However, there are a few other caveats to using the phone connection on the back of the hub briefly mentioned here in a recent topic