The slow pace of immigration checks has come under fire as Olympic officials and athletes begin arriving for the two-week Games and a leading bookmaker has already made it a racing certainty that an hour-long wait will be experienced.

Ladbrokes have set odds of 1-20 - a one pound bet would land you just five pence in winnings, plus your pound back - that any Olympian or team official will be snagged in one of Terminal Four's queues for more than an hour as they enter the country.

Ladbrokes spokesman Alex Donohue said: "It's looking certain that competitors arriving in London will be held up at the last hurdle."

With the country on a high security alert because of the Games, long lines of visitors have been forced to wait sometimes up to two hours at Britain's airport border controls.

A report in The Times on Tuesday said there were fears of public disorder at Heathrow after passengers began slow hand clapping while waiting to have their passports checked.

The report said there had even been attempts to barge through the check points as tempers frayed.

British MP Keith Vaz, the chairman of the Commons Home Affairs Select Committee, said he was "appalled" during an impromptu visit to Heathrow early on Monday morning, claiming half the passport desks had been unmanned.

"People were stuck in queues in corridors waiting to get into the arrivals hall at the busiest international airport in the world," he was quoted in The Times.

Immigration minister Damian Green said on Tuesday that staff were on target to achieve waiting times of 45 minutes for non-European Union passport holders.

"Forty five minutes is acceptable," he said after being asked to appear in front of the home affairs committee on Tuesday. "It has got better there than it was in April, May or June, but it is not perfect." (Editing by Ossian Shine)

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