I think this is the section from CAP371 that you need to be familiar with regarding night flights
Late Finishes/Early Starts
7.1.1 The conditions set in this paragraph only apply when a crew member is
acclimatised.
7.2 Sleep deprivation, leading to the onset of fatigue, can arise if a crew member is
required to report early for duty, or finishes a duty late, on a number of consecutive
days. Therefore, not more than 3 consecutive duties that occur in any part of the
period 0100 to 0659 hours local time can be undertaken, nor may there be more than
4 such duties in any 7 consecutive days. Any run of consecutive duties (Late Finishes
or Nights or Early Starts) can only be broken by a period of not less than 34
consecutive hours free from such duties. This 34 consecutive hours may include a
duty that is not an Early, Late or Night duty.
k