I had the same problem on the colder mornings, mine is a 56 plate, i understand that the have different fuseboxes on different ages.in the fuse box under the bonnet there is a row of four small black relays,2 for lights 1 for fuel pump and 1 is the power up relay(r8),this was the one that caused the problem for me. Swap it with one of the light ones to try it.this is what i did and its gone ever since!!