The Economist's Gulliver blog has a summary this afternoon about two-hour wait times at Heathrow to pass through immigration:
[O]n Saturday BAA, which owns Heathrow (but is not responsible for immigration), duly resorted to handing out leaflets apologising for the situation and suggesting that passengers complain to the Home Office.
Marc Owen, the director of UKBA [United Kingdom Border Agency] operations at Heathrow, was none too impressed by this tactic. The Daily Telegraph saw emails he sent to BAA threatening to escalate the matter with ministers, and asking it to stop passengers taking pictures of the queues. "The leaflet is not all right with us," he wrote. "It is both inflammatory and likely to increase tensions in arrivals halls especially in the current atmosphere."
The slowdown at immigration is linked to a row last autumn over passport checks. Previously, a relaxation of these checks had been agreed between the Home Office and UKBA, but UKBA ended up going further then the government had expected, and reduced staff numbers in the process. The subsequent brouhaha led to the resignation of the then head of the agency, Brodie Clark, and the reinstatement of full passport checks.
(Yes, I'm taking a break after 9 hours of requirements gathering.)