MPs are warning that Heathrow may not be able to cope with the extra passengers arriving to watch the Olympic Games.
They are concerned that long queues at immigration will harm Britain’s reputation and damage tourism "for years to come".
In a letter seen by the BBC, Culture Select Committee chairman John Whittingdale said he was concerned that not enough thought had been given to how Heathrow would deal with the arrival of ordinary passengers during the Games.
Heathrow saw a 6% rise in capacity last month, pushing it beyond 70m passengers in a 12-month period for the first time in its history.
Sent to Culture, Media and Sport secretary Jeremey Hunt, the letter said : "While visiting tourists will understand that the Olympics is a busy time, if the wait (at immigration) is in excess of an hour it may deter tourists from returning.
"The second impact may be that planes cannot unload their passengers into the terminal due to capacity being exceeded. This would lead to circling in the air, planes being left on runways or planes blocking gates."
The letter follows warnings from four airlines, British Airways, bmi, Easyjet and Virgin Atlantic that passengers could face severe disruption during the Olympics.
Whittingdale also pointed out that the proportion of passengers entering Heathrow during the Games from outside the European Economic Area was likely to be "significantly higher than usual" and each of those travellers would take longer to process than someone arriving from inside Europe.
Airport operator BAA said immigration waiting times during peak periods at Heathrow were "frequently unacceptable" and it is asking Border Force to urgently address the problem.
Shadow Olympics minister Tessa Jowell said failure to act could harm tourism "for years to come".
Border Forces said it was working with BAA to ensure it was ready to deal with extra passengers.
