Home Secretary Theresa May has launched an independent inquiry into the UK border force amid claims that guards quietly dropped certain passport checks to cope with staff shortages at busy times.
The head of the force, Brodie Clark, has been suspended and faces the sack over the relaxation of controls this summer.
Mrs May was said to be furious about the decision, although the Public and Commercial Services Union (PCSU) and Labour claimed it had been authorised by ministers.
The Home Office said she had asked the Chief Inspector of the UK Border Agency, John Vine, to investigate and will make a statement to parliament on Monday.
However, the terms of reference for his inquiry were unclear and Labour sources pointed out that his remit was usually confined to the UK Border Agency and may not cover the actions of ministers.
The Home Office would not discuss the circumstances of the changes to border checks, but reports suggest that border guards were told this summer not to bother checking biometric chips on the passports of citizens from outside the EU to ensure they are not fraudsters. The guards were also instructed not to bother checking fingerprints against a Home Office database of terror suspects and illegal immigrants, it was claimed.
Shadow Home Office minister Chris Bryant claimed that ministers had told borders staff to "cut some corners" and said Mrs May should "face the music" herself.
"It seems as if what's happened was that ministers' advice in July was actually precisely to do that: to cut some corners because there was a shortage of staff in particular between 6 o'clock and 8 o'clock in the morning and in the evening," he told Sky News.
Mr Bryant called for the publication of all the paperwork between ministers and the UK Borders Agency.
"I think we need a full inquiry in the round into all the different issues that there are here, because Theresa May can huff and puff as much as she wants and suggest that she's furious, but if the decision was hers, or if it was her decision, either about the numbers of staff that there should be at UK Borders Agency, or about the cutting of corners in the summer, then she's got to answer the questions and she's the person who has to stand up and face the music."