My thoughts would only be informed guesswork.
if I had the car physical I would plug into diagnostics and run a few checks, which is the same as what TDI North would do.
Do not expect TDI North to give you any pointers as to what the fault may be as that is how they make there money, in diagnostics and repairs.
TDI North will want you to book the car in with them for a chargeable diagnostic test.