Why will my Rover 45 2.0 diesel impression S not start?

Why will my Rover 45 2.0 diesel impression S not start? I purchased the vehicle 2 weeks ago from a dealer. It is a 2001 model. It ran fine for the first 10 miles until I hit a pot holed stretch of road. The engine gave a slight miss fire, which I put down to perhaps dirt in the tank. It then ran fine. However, this week it has started fine from cold. As soon as it warms, it surges intermittently. While driving it also miss fires intermittently. It has refused to start from warm. Yesterday it broke down some distance from home and I hadto call upon the RAC. The RAC man checked the fuel pressure by cracking open the injectors. He said the pressure was excellent. He checked over everything and said he was at a loss to finding the reason why it would not start. On the off chance we tried starting the car and it started. Hmmmm. So I drove it home. It was fine. It started again, several times. I hadto pick some stuff up on the other side of town.Drove there without problem. Started again without problem. Came up to a set of traffic lights and the engine just died before I could even start braking for the lights! It refused to start, hadto be towed home and is now as dead as a dodo on my drive way.
Has anyone else experienced this problem and if so, can they advise me or point me in the right dirrection as no one here seems to know what this fault is.