Some 1.5 million people are due to fly out of the country this weekend / PA

Cuts to immigration staff threaten to leave hundreds of thousands facing long delays

Theresa May, the Home Secretary, was accused last night of leaving Britain's borders "dangerously understaffed" as airlines warned that hundreds of thousands of Easter holidaymakers face long delays at airports.

She has been warned by 11 companies, including British Airways, that cuts to immigration-staff numbers mean they will struggle to process the 1.5 million passengers due to fly out of the country during the bank holiday weekend.

The problem is likely to resurface during the Diamond Jubilee bank holiday in June and will raise doubts over the ability of airports to cope with an influx of foreign visitors to the London Olympics starting in July.

Virgin Atlantic warned there was a "very real chance of gridlock at UK airports" and called for extra numbers of immigration staff or the reintroduction of targeted checks on travellers.

The Border Force promised to keep disruption to a minimum by deploying staff flexibly over the next five days, but insisted it would not compromise on security.

More than 370,000 passengers will fly out of Heathrow airport over Easter and another 200,000 will pass through Gatwick airport.

Mrs May was embroiled in controversy last year when it emerged that checks at airports and ports had been routinely eased by border chiefs to prevent large queues building up.

They have since been reinstalled, but the airlines are suggesting they could be temporarily relaxed in an attempt to cope with the numbers at airports.

The pressure has been heightened by continuing cuts in the strength of the Border Force, which is predicted to fall from 25,000 to 20,000 by 2015.

A spokeswoman for Virgin said: "We are concerned there is currently a mismatch between policy and resource.

"After years of reducing frontline staff, returning to a 100 per cent check system will undoubtedly mean lengthy queues at UK airports over critical holiday periods such as Easter and the Diamond Jubilee.

"If the Government wishes to continue with this policy, it must put the resource in place to make it possible or we risk gridlock at our busiest airports at a time when we hope to be welcoming millions to the UK."