Thus is what the GB warranty says on their website. It appears the hybrid transaxle is covered up to 8 years or 100k miles. Lets hope so. Toyota Ownership - Warranty | Toyota UK
Just got a call from garage (finally! after 2 and 1/2 weeks) that Toyota GB has okayed the warranty claim for a new gearbox. Will update later...
Update : Went to drop off the loan car to the garage and had a peak at the work currently undergoing to my Prius. It is now on a ramp, with its heart ripped out, ie, wheels off, engine and gearbox out, new gearbox in brown box awaiting assembly to engine. The garage manager had not seen a gearbox replacement here before, its a pretty rare sight.