Update today; first inspection reveals the threaded studs have sheared off from the engine block. They were hesitant to make any admissions but did say they weren't sure whether the nuts had been over or under tightened which suggests they're already assuming blame. Handy.
The engine is going to have to come out as they cant get to one of the sheared studs to extract it. I'll hopefully find out how bad the collateral damage is tomorrow.
I've raised a new case with VW UK customer care, informing them my solicitor will be involved if they dont resolve it to my satisfaction. Just a waiting game for now!
Good man, be firm.. Especially now the bolt missing has reared its head.