By Alex Stevenson Follow @alex__stevenson
Labour is keeping up the pressure on Theresa May over passport checks with a lengthy Commons debate on border controls this afternoon.
Shadow home secretary Yvette Cooper, leading the debate, called on the home secretary to publish her instructions to the UK border force.
Ms May repeated her denial that she had ordered the watering-down of border controls. She has blamed the border force's former chief Bodie Clark for extending relaxations contained in a pilot scheme beyond those specified by ministerial instructions.
"My pilot did not in any way put border security at risk. That was my assessment and it is the assessment of UK Border Agency (UKBA) and security officials," Ms May said.
After a number of Tory MPs intervened to challenge Labour's record on immigration, the home secretary concluded: "The public want us to reduce and control immigration and at long last they've got a government that is going to do just that."
Earlier she had been vigorously defended by David Cameron in prime minister's questions, after Ed Miliband attacked the "shambolic" way the government had handled the issue.
Yesterday Ms May insisted she would not resign after it emerged thousands of illegal immigrants, as well as terror suspects, might have been allowed into Britain because of lax passport checks.
Ms May said she was not aware an extension of the relaxation of checks had taken place, but Mr Clark responded by insisting these measures had been in place since 2008/09.
"My employer has disregarded my right to reply in favour of political convenience," he said, confirming his resignation in a statement issued on Tuesday evening.
"Despite pressure to reduce queues, including from ministers, I can never be accused of compromising security for convenience.
"This summer saw queues of over three hours (non EU) on a regular basis at Heathrow and I never once contemplated cutting our essential controls to ease the flow."
The dispute relates to a pilot scheme taking place from the beginning of June to the end of September, which relaxed some checks on those arriving from within the European Economic Area (EEA).
She has accused Mr Clark of going beyond her instructions by extending the looser checks to non-EU travellers.
Mr Clark will claim he was constructively dismissed because Ms May's statements effectively made his position "untenable". He was initially suspended last Friday.
"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 explained.
Labour want to know whether Ms May, a Home Office minister or Home Office officials signed off the operational instruction which relaxed checks on EU biometric controls.
They are seeking to establish what information was given to ministers when they decided to extend their relaxation programme, and whether any estimate was made of the number of people who would not be checked as a result of the changes.