I certainly use the 'Land After' at Heathrow, if I'm prompted by a flight crew reporting visual with the one ahead.
To elaborate on that then... I'm based abroad but fly into LGW every so often. I've had a couple of instances where it's been obvious it's going to be a very late landing clearance due to one departing ahead; in these circumstances I've asked the captain "would you accept a land-after instruction". If he's said "yes", then I've said to ATC "we will accept a 'land-after'" - the intention being to avoid exactly the scenario that someone described above, where we're almost in the flare and then someone cuts in on the radio at exactly the wrong time and we have to go around.
The question: from your point of view as an ATCO - is it more of a help or a hindrance having a pilot report "we will accept a land-after" at about 1 mile or so? Would you rather we just kept quiet rather than prompting you?
(On both occasions that I remember, what we indeed actually received in response was the aforementioned "after the departing xxxxx, cleared to land".)