So my daughter's dog has chewed through the drivers side seat belt, so i need to replace.  Does anyone know the part number and / or whether the Fabia seat belts are common with those on any other VW group cars?  Just so i know which cars to look out for on my next trip to the scrap yard.

Personally I'd just buy new. You're probably looking around £120 or so from dealer. Double check if there's seat belt pretensioners fitted? If so, disconnect battery 30 minutes before job. Used seat belts, there's no history, could be goosed although look visually fine. Did the same job on my wife's Audi A2, not because of a dog, but they failed to retract properly. It's a key safety feature so why compromise?

The pre-tensioner is fitted to the plug-in part though, I believe. Swapping the actual belt should be ok I would have thought? 

15 minutes ago, mrgf said:

The pre-tensioner is fitted to the plug-in part though, I believe. Swapping the actual belt should be ok I would have thought? 

Could very well be. On my wife's A2 (long since gone) it was in the seatbelt mechanism.