As I suspected it was the lambda sensor. Picked it up last night after the dealer mucked about sorting it out. To cut a long story short I bought it from Virgin and have a service card, 2 yr warranty - now expired, dealer got Renault to pay half

and waited for a decision from service card people if they would pay rest, yeah right! Buy the time request was denied and they then spoke to me for my approval, it was too late to get the part and fit it on Monday night.
Just waiting for usual Reg Vardy customer satisfaction call!
Rich