Geraint, what code was thrown by the computer (should be written on the sheet you got from the work on the car). Give us that and we should be able to give you a lot better answer. There can be a lot of things that can cause this sort of thing. I am assuming your engine did not quit, it simply went into "limp mode" and it was just severely down on power. This is a normal reaction for when the computer thinks the engine is running too warm. if this is the case, then other looking needs to be done as it could also be simply low coolant, bad water pump, etc in addition to the computer possibly causing problems.

 

What did you temperature gauge do? I had a similar issue with my 03 shortly after I bought it. Driving along just fine when the temp gauge pegged hot, car immediately went into limp home mode. I pulled over called Jaguar (I wasn't real nice)...started the car and it was fine...for about 5 miles then it did the same thing. They replaced the temp sensor, then about 2 months later I was driving along and the temp guage pegged H again...but it did not go into limp home mode this time. I figured if the bloody engine blows up I'll get Jag to put in a new one..but nothing happened. Took it to the dealer and they replaced the thermostat and no recurrence.