Theresa May will today be asked to reveal how many suspected terrorists and criminals were allowed to enter Britain during the recent fiasco at the UK Border Agency (UKBA).
In an emergency House of Commons statement, the Home Secretary will insist that the security lapse this summer had nothing to do with the spending cuts that will lead to 5,300 jobs being lost at the UKBA.
Mrs May, facing potentially the biggest headache in her 18 months at the Home Office, will insist that the usual controls at Heathrow Airport and Calais were dropped by senior officials without ministers being told or giving approval. But Labour and the trade unions believe the cuts played a part.
The immigration service is braced for yet another scandal this week. A senior official is due to appear in court over claims that he took bribes to allow Nigerians to enter Britain illegally.
Three other officials were suspended, including Brodie Clark, the £130,000-a-year director of the border force, after Mrs May was told that strict security checks were scrapped in July for people from outside the EU. This meant they did not face fingerprint or biometric checks – to see whether their passport photograph was the same as the one electronically stored by the Home Office – and staff did not check if the individuals were on a "watch list" of terrorists and criminals.
In a pilot scheme, the microchip passport checks were halted for people with UK and EU passports, but should have been retained for others.
Last night Labour demanded to know whether anyone on the watch list had been allowed into Britain – and whether they had now been arrested or removed.
In a letter to Mrs May, Yvette Cooper, the Shadow Home Secretary, said: "The first, and crucial step, must be to ascertain the implications of the lapses in security. In particular, we need to know whether anyone posing a threat to Britain's national security was allowed to enter the UK during the period when the decision of ministers to relax passport checks was taken further than the Home Office has said was ordered."
Ms Cooper said terrorist suspects had been seized in Calais in the past.
"We need to know if someone on a watch list entered the UK during this time, and for the police and security services to take the necessary steps to protect the public," she said.
The Shadow Home Secretary asked why it took four months for ministers to discover controls had been watered down – when some staff complained it had happened in August.
Ms May will brief MPs on the independent inquiry she has ordered into the affair by John Vine, chief inspector of the UKBA. Labour will call for him to consider the impact of the cuts.
This is the latest crisis to engulf the immigration service. Five years ago, John Reid, the then Home Secretary, dubbed it "not fit for purpose". Under Labour, its problems led Home Secretary, Charles Clarke, and Immigration Minister, Beverley Hughes, to resign.