Hi Lissart,
From
http://www.caa.co.uk/docs/33/CAP413Supplement.pdf
"‘Land After’ Clearance
A landing aircraft may be permitted to touch down before a preceding landing aircraft, which has landed, has vacated the runway provided that:
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
It is during daylight hours;
The preceding landing aircraft is not required to backtrack in order to vacate the runway;
The controller is satisfied that the flight crew of the landing aircraft will be able to see the preceding aircraft which has landed, clearly and continuously, until it has vacated the runway; and
The flight crew of the following aircraft is warned.
Responsibility for separation rests with the following aircraft."
Once visual and if you don't receive landing clearance by say CAT 1 limits of 200ft, and you've been advised that it will be a late landing clearance - then it's down to your judgement on how the separation looks.