FTTC on an extension

I realise that it is a rather unorthodox but I was wondering if it would be possible to feed an extension with both VDSL and POTS by connecting the two ports on the front of the NTE5 master socket with a patch cable?

technically yes but you would cause issues for the vdsl. You may be better off pushing the vdsl (via the internal krone strips on the filter plate) down a spare pair of the extension cable and connecting that up to an ethernet socket at the other end.
Of course - much better if you just ran a cat 5 extension purely for the vdsl or sacrifice pots on an extension by terminating that onto the vdsl plate.

actually it would be easier to remove the faceplate and go back to micro filters. But you will degrade your service and will be charged for any callouts when the facep[late is reinserted / replaced.

technically yes but you would cause issues for the vdsl.

What sort of issues? If it's just a case of a small drop in speed due to the extra cable length I could live with that as it would still be substantially more than the 2Mb ADSL I have at the moment.

Of course - much better if you just ran a cat 5 extension purely for the vdsl...

That would have been my preferred method but running cat 5 from the master socket is turning out to be problematic and moving the master socket is not possible either.

running a simple patch cord would leave the circuit unfiltered. Also the extension wiring will cause reflections which are more noticeable on vdsl than adsl - reducing speed and reliability. Also do it wrong and you could cause loop issues.
Of course going back to micro filters and removing the vdsl plate will have similar issues but is far cleaner and cheaper way to do it. Will probably work ok.