Pressure is mounting on Home Secretary Theresa May after the head of the UK border force quit and accused her of misleading Parliament.
In a scathing parting shot, Brodie Clark flatly denied "improperly" extending a relaxation of entry controls and said he was suing for constructive dismissal.
He said Mrs May had blamed him for "political convenience" and made statements to MPs that were "wrong".
The dramatic intervention was swiftly countered with a statement from the UK Border Agency insisting Mr Clark had admitted going beyond ministerial orders.
But it increases the heat on the Home Secretary, who has already been forced to insist she will not resign over the issue. She is due to face another grilling in the Commons after Labour called an Opposition Day debate.
David Cameron's support for his Cabinet minister is also expected to be tested when he takes Prime Minister's Questions.
Giving evidence to the Home Affairs Committee, Mrs May said she had authorised piloting the easing of some border checks on EU travellers over the summer, partly to reduce queues. But she insisted Mr Clark had gone further by scrapping key checks against a Home Office database without ministerial approval. "Those wider changes were ones which I rejected," she said. "I take full responsibility for my decisions and actions related to the pilot, but Brodie Clark must take responsibility for his actions."
Three senior staff, including Mr Clark, have been suspended and those responsible will be punished "to make sure that border force officials can never take such risks with border security again", Mrs May said.
However, in a statement Mr Clark hit back and announced he was leaving his job. "I am anxious to take part in any independent inquiry into matters relating to UK Border Agency but my position at UKBA had been made untenable because of the statements made in the House of Commons by the Home Secretary Theresa May," he said.
"Those statements are wrong and were made without the benefit of hearing my response to formal allegations. With the Home Secretary announcing and repeating her view that I am at fault, I cannot see how any process conducted by the Home Office or under its auspices can be fair and balanced."