I have not done anything more as yet since I posted the question, It was fully serviced (all filters, plugs etc) in March 2012 and has not been any problem until now.
The engine management light is not on, except when I cleaned the map sensor but that has gone out now and not come on since.
The local garage didn't have a clue (normally they cannot be faulted) and tested the alternator, as this was replaced at the same time of the last service, and this showed no problems as the car still had the fault without the wiring attached to the alternator.
I have also connected the engine direct to earth and that has no effect.
It has around 60000 miles on it.
When the engine cuts out, the battery light flickers on and there is a click but goes straight out when the engine restarts itself.
Also there is a clicking after you turn the engine off which is coming from somewhere near to the throttle cable assembly.
As mentioned I took it to the garage when it was cold and it ran lovely until I tried to give it more revs and obviously cut out between 3000/4000 revs.
I had to leave it over night to cool down as after they were testing it on the diagnostic machine it was too warm to get back as it will not rev past 1000/1500 when it is warm.
Again it ran lovely on the way back until you hit the point where it cuts out.
It starts on its own immediately after it has cut out (within a split second).
If you take your foot off the accelerator just after it has cut out/restarted the revs go up to where they would be expected and then drop to around 800 for normal idling, dropping at a normal speed(not slowly dropping - just how you would expect them to drop)
Hope you can help.