My BIL arrived at Heathrow last night on a flight from the Far East. At some later point in the flight they were informed that Border Agency staff would be coming on board to check passports after landing.
They didn't.
He finally disembarked and more than an hour's wait later, BIL and wife got back into the UK. I won't repeat his comments here because they are easy to guess.
Heathrow isn't functioning now by any normal standards and it won't be during the Olympics, either.