Brodie Clark, the head of the UK Border Agency (UKBA) has quit over the relaxed passport check row, accusing Theresa May of misleading the public. He says that he plans to lodge a claim for constructive dismissal.

Suspended from his job last week, he faced the prospect of disciplinary action and even the possibility of criminal charges. Making it very clear she had no intention of resigning herself, the Home Secretary said "Brodie Clarke must take responsibility for his actions".

In a strongly worded statement, Clark 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.

He added that he had full authority for all the actions he had taken, disputing May's account that officials acted without her authorisation:

The Home Secretary suggests that I added additional measures, improperly, to the trial of our risk-based controls. I did not. Those measures have been in place since 2008-09.

The Home Secretary also implies that I relaxed the controls in favour of queue management. I did not. Despite pressure to reduce queues, including from ministers, I can never be accused of compromising security for convenience.

Queues at Heathrow this summer regularly lasted in excess of three hours, but dsepite this, Clark said "I never once contemplated cutting our essential controls to ease the flow."

On one point, Clark and May are agreed -- and that is on the efficacy of risk-based checks. Appearing before MPs on Monday, May insisted that intelligence-led checks had actually boosted interceptions of illegal migrants by 10 per cent. She claimed the problem came when Clark went too far by relaxing checks on passengers coming from outside Europe. Clark, pointing out he had been arguing for such schemes since December 2010, said:

The evidence to support [intelligence-led checks] is substantial and the early findings are encouraging. I would do nothing to jeopardise them. I firmly believe that a more fully risk-based way of operating will offer far greater protection to the United Kingdom.

As I argued yesterday, an effective system must operate with varying degrees of stringency. It will be a shame if moves in that direction are halted because of a knee jerk reaction to this row.

It was never certain that May would be able to ride out the storm, and Clark's decision to speak out shows that he is not willing to be scapegoated. He will now appear on Tuesday before the Commons home affairs select committee. Keith Vaz, the Labour head of the select committee, told the BBC: "It's completely contradictory to what she said. This is a complete turnaround of events." May remains defiant; it will be up to the committee to determine whose account is accurate.