MPs have questioned Heathrow Airport's ability to cope with this summer's Olympic Games.
Planes could be "left on runways" for long periods and tourists could be deterred from returning, warned the House of Commons Culture, Media and Sport Committee.
The concerns were expressed in a letter - leaked today - from the committee's chairman, John Whittingdale, to Culture Secretary Jeremy Hunt.
In his letter, Mr Whittingdale said two of his committee's members - Therese Coffey and Gerry Sutcliffe - had attended a briefing by Heathrow operator BAA concerning the company's preparations for London 2012.
Mr Whittingdale said they had reported back that, while BAA considered the big challenge was the departure of spectators at the end of the Olympics, the two MPs "did not leave the briefing confident that Heathrow was ready to cope with the arrival of a huge number of competitors, Olympic family and visiting tourists in timely fashion".
The letter went on: "We understand that significant preparations have been made to accommodate unusual sporting equipment, special lanes for the Olympic family, welcoming arrangements for competitors and additional Olympic ambassadors.
"However, far less thought seems to have been given to the issue of how to deal with long queues at immigration.
"The UKBA (UK Border Agency) representative suggested that there was insufficient funding to ensure all passport stations would be open."
Mr Whittingdale went on: "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."
He continued: "We also understand that the flight schedule is not changing in any way and there was no suggestion that any contingency has been made for, perhaps, extra time being made to remove items from aeroplanes or for the unloading of passengers.
"Furthermore, the proportion of passengers entering Heathrow from outside the EEA (European Economic Area) may be significantly higher than usual. Again, this takes longer to process through immigration."
BAA said today: "The concerns raised in the committee's letter relate to immigration, which is a matter for Border Force and the Home Office.
"Immigration waiting times during peak periods at Heathrow are frequently unacceptable and we have called on Border Force to address the problem as a matter of urgency. There isn't a trade-off between strong border security and a good passenger experience - Border Force should be delivering both."