Can't thank everyone enough for the replies.

My friend has been pressurised by the garage, and his own need for the car and has agreed to fund the cost of repairs himself. The garage have got a clutch for under £400 which seems good.

Box is already at a gearbox place, so will be rebuilt at a cost of £1100 Then all the labour on top, which I have told him should be not much more than 6 hours max.

He'll continue the fight with the warranty company, but seems like it's not worth the paper it's written on