Home Secretary Theresa May was accused of leaving the UK's borders “dangerously understaffed” today as airlines and airports warned of “unacceptable” delays over the Easter weekend.
Shadow immigration minister Chris Bryant said Government cuts to Border Force staff were "leaving the security of the UK exposed".
But the Border Force insisted there would be no compromise over security, saying they aimed "to keep disruption to a minimum by using our staff flexibly to meet demand".
It came as airlines warned the Home Secretary that Britain "risks gridlock" at airports over the Easter break due to staff shortages.
British Airways and Virgin Airlines are among 11 firms that have written to Mrs May in anticipation of "unacceptable" delays to hundreds of thousands of passengers travelling over the long weekend.
Mr Bryant said: "It is time that the Home Secretary came clean about the security at our borders.
"Her cuts to staff have seen passport queues lengthen, not only leading to delays for passengers but also leaving UK Border Force staff with a difficult decision of whether to relax security to alleviate congestion and risk allowing people to enter the UK without being properly checked.
"With a cut of over 5,000 staff promised by the next election, the Home Secretary is leaving our borders dangerously understaffed, just when the UK is expecting record numbers of arrivals for London 2012."
He went on: "We've already seen hundreds of arriving passengers waved into the UK at Birmingham airport and now 11 major airlines are saying what we've said all along: UK Border security is of the utmost importance and by undertaking these staffing cuts, this government is leaving the security of the UK exposed.
"The Home Secretary must now ensure adequate staffing levels are put in place during the Easter and Royal Jubilee bank holidays, and in good time for the summer games, to make sure border staff don't find themselves in the same situation as they did last summer when thousands flooded through the border, without being fully checked on the orders of the Home Secretary, under her own pilot scheme.
"Our national border security is paramount, as should be our ability to safely welcome thousands flocking to the UK for the Olympics, but Tory-led Government is putting this at risk with under-resourced passport controls at our ports and airports."
The Border Force is under fire for a lack of staff able to carry out full security checks, which the airlines say must result in a recruitment drive or the relaxing of some of the more stringent measures currently in place.
A spokeswoman for Virgin Airlines said: "While the decision on what level of check should be made at the border is, of course, a matter for government, we are concerned that there is currently a mismatch between policy and resource.
"After years of reducing frontline staff, returning to a 100% 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."
More than 370,000 passengers will leave Heathrow airport between Good Friday and Easter Monday, and 200,000 will pass through Gatwick.
A spokesman for Heathrow owner BAA said: "Immigration waiting times during peak periods at Heathrow are currently unacceptable and we have called on Border Force to address the problem as a matter of urgency."
A Border Force spokeswoman said: "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."
The Border Force spokeswoman added: "The Border Force is prepared for the busy Easter period and has ensured extra staff will be working at the border to carry out vital security checks."
But no details of the numbers of extra staff on duty were released and it is understood the measures are part of contingency plans for busy periods.