Ford Focus engine cuts out after a couple of miles in damp conditions; restarts after 10 minutes

Background: last bank holiday weekend - drove 300 miles Saturday/Sunday - some jams, some fast motorway. Heard a couple of clunking sounds at slow speed which I thought was road surface at time. Reached destinations fine.
Car not used on Monday. 8am Tuesday, tried to drive to work in rain. Started fine but after 2 miles heard clunking sounds, car lurched; engine management light came on; cut out on braking at roundabout. Wouldn't restart. Needed help to push up onto verge. Did restart after 10 minutes but I didn't want to continue in rush hour traffic. Drove it to nearest garage later without incident; they could find nothing wrong. Next time I used it there was one clunking sound but car didn't falter and I got to destination(5 mile trip). For the next week I drove it to work, 5 miles each way in moderate town traffic, without any unusual sounds or problems. Today on driving home from work, car started fine in heavy rain and I got a couple of miles before it died on me suddenly when braking at junction. Wouldn't restart for about ten minutes. Drove another couple of miles OK, then thought it was about to cut out, so parked it in a side road a mile from home (lost confidence as last part of journey home involves queueing up to cross a very busy dual carriageway).