MATS part 1, section 2, chapter 1, part 15
When aircraft are using the same runway, a landing aircraft may be permitted to touch down before a preceding landing aircraft which has landed is clear of the runway provided that:
a) the runway is long enough to allow safe separation between the two aircraft and there is no evidence to indicate that braking may be adversely affected;
b) it is during daylight hours;
c) the preceding landing aircraft is not required to backtrack in order to vacate the runway;
d) the controller is satisfied that the landing aircraft will be able to see the preceding aircraft which has landed clearly and continuously, until it has vacated the runway;
and
e) the pilot of the following aircraft is warned. (Responsibility for ensuring adequate separation rests with the pilot of the following aircraft.)