I drove my Focus at high speed and the Engine Management System (EMS) light began to flash and the engine began to stutter. Without stopping the engine, I tried to drive off the motorway but the engine just died on the hard shoulder. I restarted the engine, the EMS light went out and I was able to drive 35 miles to a Ford dealership with no problems.

The dealership did a "diagnostic" on the car and found that the fuel filter (replaced in the previous 2 years) needed to be replaced and they did this. I drove a further 450 miles including motorway driving hassle free. On a later journey at high speed, the car gave a large stutter and the EMS light came on again although the engine did not cut out. I took the car to another dealership and they checked the filter but found no problems with it but replaced it yet again.

When I got home, I took the car to my local independent garage who carried out an electronic diagnosis but found no error codes. I had the car checked and serviced anyway and set off on a hundred mile journey. 60 miles into the journey, the car started to stutter mildly so I pulled off the motorway, switched off the engine and restarted it. I went beautifully for the latest 200 miles.

I don't want to be paying £60 or £70 for diagnostics which reveal nothing wrong. What should I do.