Whats wrong with my corsa?!?

Hi i have a 52 plate 1.2 corsa sxi. Has recently had the clutch, timing chain, filters and spark plugs changed before i brought it however, 3 days into owning it the car started to take ages to start up from cold - i.e after it has been stood for more than 2+ hours the car will tick over for about 8-10 seconds before catching and starting up, if the car has been driven and then is left for 5 or 10 minutes before starting up again it will start first time.
I took it to a garage who plugged it in and said the codes coming up were for an engine misfire (turned out to be a problem with the coil pack which was replaced) and the crank arm sensor which was also repalced. Drove home in it lovely jubbly but go to start the car up again the next day and the exact same problem happens, despite having just parted with the best part of £200!
When the car is being driven you wouldnt know anything was wrong with it, drives lovely and smooth and isnt sluggish at all, its just the trouble starting up when its cold. Have read somewhere that it might be a bad one way valve in the fuel pump but am loathe to take it to the garage again to get fleeced for more money and still have the same problem - any ideas?