Cuts to the UK Border Force led senior officials to reduce the number of checks at ports to manage the build-up of queues of people waiting to enter the country, shadow home secretary Yvette Cooper has claimed.
She accused Home Secretary Theresa May of not knowing which airports had introduced her pilot scheme to relax checks for European Economic Area (EEA) residents entering the UK, while she had also failed to detail how many foreigners linked with crime and terrorism had passed through the country's borders undetected.
Ms Cooper said the pilot was "not just one Thursday a month at Luton" but had been rolled out across the country, with potentially millions of immigrants subjected to reduced checks at the country's ports.
An internal email from the UK Border Agency revealed that senior staff could only authorise back-up at border controls if staff had already reduced the level of checks, she added.
Mrs May also faced "serious allegations" from the former head of the border force Brodie Clark that he did not act without ministerial authorisation amid claims Mrs May's officials had dismissed the civil servant as a "rogue official".
Speaking during an Opposition Day debate in the Commons, Ms Cooper said the real reason for the "fiasco" was that the number of employees manning the border had been cut by 1,500, making it impossible for staff to carry out advanced checks and keep queues down at the same time.
She said: "We are seeing now that the scale of these cuts is putting pressure on the Border Agency just like the scale of cuts to policing is putting pressure on community safety.
"People across the country now fear that corners are being cut and border security is being put at risk by the scale of the Government's border cuts as well.
"This needs to be sorted out. We had the embarrassing spectacle of a Home Secretary who does now know what she agreed to, how its being implemented or how great security risks have been. The most shocking thing of all is that they do not seem to know what has been happening on their watch."
But Mrs May hit back, claiming that Ms Cooper had developed a "sudden interest" in immigration as it was not usually a subject Labour wanted to talk about.
She added: "I have to say it's a bit rich from a party that gave us 2.2 million net migration, the foreign national prisoner scandal, Sangatte, 450,000 asylum backlog, no transitional controls with eight eastern European countries, the Human Rights Act and a points-based system that fails to reduce immigration.
"I am willing to welcome any convert to the cause of controlling immigration."