Citroen C4 engine dies when pulling away

Hi, I own a 2008 Citroen C4 Grand Picasso 1.8VTR+ It has 18000 miles on the clock.
The engine starts without any problem, ticks over smoothly when above 2000rpm pulls ok. The problem I have is when the engine is when pulling away, particularly from cold, the engine looses power, it feels like it is firing on 2 or 3 cylinders, I have to depress the clutch then ease the revs up to pull away, once it is up to speed it runs fine. I occassionaly get the service light come on with a handbrake fail warning followed by a depollution sensor fault, when I turn the engine off and restart it the faults dissappear. My local independent garage has looked at it, the only fault code they could find was a missfire at high revs, they changed the plugs which were mucky but other than that they could not find anything wrong. Any advice would be welcome. Thanks