ok so I replaced my clutch last week and everything was running smooth

and I drove from cairnryan Scotland down to Doncaster 246 miles all was well until I pulled off the a1 and suddenly no power and the engine cut out and I rolled to a stop the battery light was on the dash and that's it, tried to turn her over once at stand still and nothing so I took the keys out of the ignition then tried again and she started up again fine but I have noticed in the morning lately turning the car on seems to be a real pain ie keys in wait for engine prep then turn the key to start... it starts but it only goes to about 500 revs then down then up until I put a bit of pressure on the accelerator pedel and it eventually springs into life.
no fault codes
could this be down to the cold weather or do you think there is an underlying problem?
thanks in advance