[Mr Whippy]

Was driving and the drivetrain warning came on saying power had reduced. Car was running rough and stalled while at a set of lights. Managed to start again and get to the side of the road and got it towed.

Garage has confirmed there's metal shavings in the oil due to low oil. Oil change was done about 2k miles ago a few months ago and had been running perfect until then.

So did it have metal shavings at last service?

If not, they're new. But seemingly caused by low oil?
So is the car currently low on oil?

Something isn't stacking up with the failure mode this garage is describing, and the list of events described.

Personally I'd be making sure no one is arse covering for a bad job... assuming it's the servicing dealer who now has the car.

Good luck with it any way!