Pressure was mounting on the Home Secretary, Theresa May, last night after private memos emerged which showed that full biometric checks were waived hundreds of times over the summer as border staff struggled to cope with queues at ports and airports.
The Home Secretary had previously refused to say how often full checks were abandoned during the period, although she revealed that 28 ports and airports had been involved in the pilot scheme under which controls were eased.
Internal UK Border Agency (UKBA) emails leaked to Labour showed full checks were relaxed on 100, 165 and 260 occasions in individual weeks, implying they were eased more than 2,000 times during the pilot scheme before it was scrapped.
Leaked documents also disclosed that passengers on private jets had routinely been allowed into Britain without passport checks for months.
The emails reveal that immigration staff were worried about the relaxation of checks on private jets arriving at Durham Tees Valley airport. The policy meant passports were not examined and officials were not being "allowed to physically see the passengers" who were also not checked against lists of terrorists and international criminals.
One union official complained in March: "It would seem that you are relying on the fact that anyone operating a private charter has the best interests of the UK at heart and will therefore always declare everyone and everything on board." Management replied that the practice was "in line with many airports across the country".
In June, officials complained of a "situation where we are not able to secure the border as robustly as we would like to, for no justifiable reason". The following day they were told a new national risk-based approach to handling private flights was being brought in across the county.
The revelations come as former UK border chief Brodie Clark is due to appear before the Home Affairs Select Committee today.
Ms May has accused him of extending her pilot and relaxing controls on non-EU citizens without her permission. Mr Clark has rejected her claims and quit his post to set out his version of events. He is expected to insist that he only ever eased passport controls to non-EU citizens on police advice.
Yvette Cooper, the Shadow Home Secretary, said: "Ten days on, there are even more questions than answers about what on earth was going on at our borders this summer.
"Last week the Home Office wouldn't admit to having figures about how often checks were downgraded. Now we know those figures exist."