Wirbelsturm,
I need to correct a misnomer. It appears you are confusing "credit hours" and "flying hours". There is an important distinction.
A BA pilot at LHR is contracted for 1045 credit hours. This includes leave, simulators, other duties, etc. This is not to be confused with flying hours for which you are not specifically contracted. The way credit per trip is calculated varies and is not strictly to do with the number of flying hours on a particular trip (there is some weighting to recognise low hours days for example - ie. on shorthaul, you are guaranteed a minimum of 4:30 credit hours per day worked).
In practice, this means a longhaul pilot achieves around 850 flying hours and a shorthaul pilot will achieve 700-750 flying hours per year whilst both achieve the annual CAP (credit hours) of 1045. Those hitting 900 flying hours will generally have done some overtime.