Car in gear but no acceleration, press accelerator, no response whatsoever, but idles?

I have had for a few months now, with no series problems. Last week drove to london, got there, stuck in stop start usual london, trouble starts, car in gear but no acceleration, press accelerator, no response whatsoever, but idles. Switch off and start again. Car drives fine for another 10mins, at the same time the engine management light comes on. Then again. No revs, just idling in gear no matter how much I press the accelerator, simply going nowhere fast. Switch off and start again, that was the last time the symptoms displayed, its been a few days driving about and drove from london 140miles+. No symptoms has shown since
any clues what this could be?