Citroen Xsara Picasso Won't idle, no power.

Car starts but cuts out immediately, needs lots of revs just to keep it idling.

Drove home from work (20 miles) and the car was fine, there was nothing unusual about the journey. I stopped at my office for about twenty minutes, when I restarted the car it cut out (a bit like when it is hot in the summer and the ac is on), so I restarted again and gave it a bit more revs to keep it going. It was a 3 mile drive home with a little bit of traffic. Cut out at the traffic lights half a mile from home and needed a lot of revs after that to limp the rest of the way.

There were/are no warning lights on the dashboard. Has had a recent service and MOT (last month). Put £20 of petrol in 3 days ago and have done about 80 miles since then, still two bars showing. It doesn't feel like dirty petrol (have had that experience previously).

I'm fearing the worst, but is there any chance that it could be something simple?