Download FS Real Time from SimV. It'll keep your FS clock sync'd with the real world time, and also take into account timezone changes if you're on a longer flight.

I didn't have much success with Real Time(in fact zcottovision prompted me to go back and clean up the residue)and I'm not fussed when I fly in FS. I don't get home from work until 4-5PM and have no intention of doing all night flights so I subtract 8hrs on local time,note the time I land,add an hour(turn around time),reset the clock and go flying. If you go to SETTINGS and set SYSTEM TIME for your location you'll at least start with your own local time when you next go to fly.

I have found that if I save a flight at an airport in my timezone, and then make this my default flight, the time will always stay correct based on my local.

So if you live in the UK find an airport that is close to where you live and use that airport as your default starting point.  I think FSUIPC has a fix for this also, it is in the technical menu somewhere, but not sure about that part.....