Sorry about the confusion it is a C5 Tourer.

Anyway, I have today been across to another dealer at the request of Citroen UK. They were very helpful and brought out the Senior Technician who told me that as soon as he heard that the car was not changing from 4th gear into 5th and 6th he knew it was the tyres. To back up his theory he produced a ring binder with updates delivered by Citroen to Senior Technicians on any new faults that arise when their cars have been in service for some time. And not covered in the normal manual. The problem only occurs in certain C5 gearboxes (not all), and will occur if the tread is low (3mm and below) or different tyres to those already in place from the factory (Michelin 225, 45, 17, 97W). Although there is no advice given in their handbook supplied with the vehicle, a sticker on the offside door column displays what tyres are fitted along with correct pressures. Citroen Customer Services say that this is enough for them to demonstrate that they advise only this tyre should be fitted. They have also told me that if the current tyres are not replaced with the correct ones when the vehicle is returned at the end of the lease period, they will make a charge accordingly. Their argumant has, I feel, so many holes in it, but they are not budging from their position.

They will not give me a copy of the updated fault diagnosis that the senior technicians hold, nor the date on which it was issued. Nor will they say why the tecnician from the original dealership failed to inform me of this problem when he had the car in to deal with the fault on 2 occasions in April and May. This is despite the service department trying to get me to change my front tyres (albeit that they had a few millimetres of thread left) on both occasions.

Is there someone out thre who can give me some advice either about Citroen, the problem itself, or any legal position?

Michelin suggest fitting new tyres to the rear so I'd suggest swapping front and rear tyres and see what happens.