British lawmakers have questioned Heathrow Airport's ability to cope with an influx of passengers during the London Olympics this summer, warning that long lines at immigration could force planes to sit on runways or even circle Europe's busiest airport.

The concerns were expressed in a letter to Culture Secretary Jeremy Hunt from the chairman of House of Commons Culture, Media and Sport committee, John Whittingdale. It was published Wednesday.

Whittingdale wrote that lawmakers had met with Heathrow operator BAA on its preparations for Olympic games and "did not leave the briefing confident" that Heathrow was ready to cope with huge numbers of arrivals around the Olympics in a "timely fashion." The games run from July 27 to Aug. 12.

"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," Whittingdale wrote. "However, far less thought seems to have been given to the issue of how to deal with long queues at immigration."

Whittingdale said those lines could push terminals over capacity, forcing planes to circle in the air, sit on runways or block gates if they can't unload their passengers.

Last year, even without the crush of the Olympics, Britain's former border chief relaxed some passport checks during the busy summer tourist season just to handle the demand.

Long immigrations waits could deter tourists from returning to Britain, Whittingdale added.

Heathrow typically handles an average of 190,000 passengers arriving and departing each day, with 69.4 million total in 2011.

BAA noted that Whittingdale's concerns related to immigration — which is the U.K. Border Agency's responsibility — and criticized the agency.

"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," BAA said. "There isn't a trade-off between strong border security and a good passenger experience — Border Force should be delivering both."

The U.K. Border Agency responded to the letter by saying it is "well prepared" for the Olympics and has additional staff available for busy periods.

"We will not compromise on border security," it said.

The day after the closing ceremony — Monday, Aug. 13 — is set to be the airport's busiest ever, BAA estimates, more than its previous record of 233,561 passengers on July 31, 2011. Heathrow is forecasting it will handle 35 percent more baggage for departing flights on Aug. 13 than on a normal day, which sees about 150,000 items.

Heathrow is creating a special terminal for Olympic athletes, coaches and sponsor to fly out of Britain after the end of the games. Airport officials say 10,000 athletes and support staff will go through the "Special Games Terminal" in the three days after the closing ceremony to process the exodus.