A number of airlines have issued a warning to the Home Secretary that Easter getaway travellers could face 'gridlock' at airports due to immigration staff shortages.
A total of 11 airlines, including British Airways and Virgin, have told Theresa May that passengers face lengthy queues as the UK Border Agency does not have the resources to carry out the stringent passport checks.
Travel organisation Abta said that around 1.5 million people would be heading off abroad for Easter.
More than 370,000 passengers are expected to leave Heathrow Airport between Good Friday and Easter Monday, and 200,000 will go through Gatwick.
The airlines say that many of those travellers will face "unacceptable" delays because of a mix of strict passport controls and a lack of resources.
According to the Daily Telegraph, a leaked Virgin Airlines memo read: "If arriving passengers are unable to proceed efficiently through the UK border then the entire airport operation will be at risk. Passengers arriving late from passport control to collect their luggage will cause congestion in the baggage hall, delaying delivery of luggage from later flights.
"If there is no space in the immigration hall for any more arrivals then airlines will be forced to keep passengers aboard the aircraft, thus jeopardising the operation of subsequent flights.
"This in turn will delay departing passengers and cause overcrowding in departure areas as a result."
The airlines would like to see the Government employ more border control staff or relax tough restrictions on immigration checks.
Simon, chief executive of the British Air Transport Association, wrote to Theresa May on behalf of the 11 airlines, and told the Daily Telegraph: "We don't want to see queues at airports. It's bad for passengers and for UK plc to see long queues at passport control.
"We are looking for reassurance from the Home Office that the Border Force will be properly resourced. We don't want to see queues at airports."
A Border Force spokeswoman told the Independent: "We will not compromise border security, but we always aim to keep disruption to a minimum by using our staff flexibly to meet demand.
"Carrying out full checks at airports help us stop threats from terrorists, criminals and others who want to harm the UK and make sure that only those with the right to enter the UK can do so."
A spokesman for Heathrow owner BAA said there should not be a "trade-off" between strong border security and a good passenger experience, but that the UK Border Force "should be delivering both".
Meanwhile, hundreds of passengers at Birmingham Airport were last week allowed to enter the UK without proper passport checks after a computer power failure rendered electronic scanning impossible.
The immigration system failure saw around 200 travellers walk straight through security on Thursday after being delayed for three hours.
The incident occurred after around 500 passengers were allowed to the enter the UK without their passports being checked last Wednesday night in a bid to relieve pressure on arrivals, a move that saw senior Border Force officer David Dodds suspended.
Sign up to our weekly newsletter | Follow us on Twitter | Become a fan on Facebook