The border force chief quit and launched an outspoken attack on Home Secretary Theresa May on Tuesday in a row over the easing of passport checks at ports and airports that has led to fears that national security may have been compromised.
The government suspended Brodie Clark and two of his senior staff last week after it discovered some passport controls had been abandoned.
The furore threatens to engulf Prime Minister David Cameron's government in a fresh crisis over the conduct of a minister just weeks after Defence Secretary Liam Fox quit over a close friend who falsely claimed to be his official adviser.
May said earlier she had no plans to resign and won the backing of Cameron, who joined her in pinning the blame for lax border controls on officials exceeding their authority.
UK Border Force chief Clark said May had made his position untenable by telling parliament he had relaxed controls without her permission.
Those statements are wrong and were made without the benefit of hearing my response to formal allegations, he said, adding that he would be seeking damages for constructive dismissal.
With (May) announcing and repeating her view that I am at fault, I cannot see how any process conducted by the Home Office under its auspices, can be fair and balanced, he added.
May said on Monday that Britain would never know for certain how many suspected terrorists and serious criminals were waved into the country since July, when she said border officials unilaterally suspended some checks.
The lapses in Britain's border controls are embarrassing for Cameron's ruling Conservatives, who are traditionally strong on law and order and have pledged to drastically reduce the level of net immigration to just tens of thousands a year.
Speaking to a parliamentary committee on Tuesday, May said she had authorised a limited easing of passport checks for European Union nationals in a pilot programme, but border guards had gone further without permission.
The pilot that I authorised did not in any way put border security at risk, May said, adding that she had not discussed her scheme with Cameron or the cabinet as it was an operational matter.
Speaking at a later parliamentary hearing, Cameron said May's pilot scheme appeared to have been successful in focussing resources on higher risk individuals.
It's also clear that there was activity going on by the UKBA (UK Border Agency) that was not acceptable, he said.
The disclosures come just months before London is due to host the 2012 Olympics, raising concerns that criminals or militants may have been able to enter Britain at a time when security was meant to be a priority.
(Editing by Jon Hemming)