It's no exaggeration to say that today's events could determine Theresa May's political future. Brodie Clark, the former head of the UK Border Force, who has accused the Home Secretary of misleading parliament over the border control row, is appearing before the home affairs select committee at 11:30. In the statement he made when he resigned last Wednesday he said that May was "wrong" to accuse him of taking "additional measures" beyond those agreed with ministers to reduce risk-based passport checks.

He added:

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. 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.

Significantly, however, May's account is supported by Rob Whiteman, the chief executive of the UK Border Agency (of which the Border Force is part) and Clark's old boss. Whiteman, who is also appearing before the committee today at 12pm, claimed that Clark admitted to him on 2 November that "on a number of occasions this year he authorised his staff to go further than Ministerial instruction". He has since faced claims that he was "strongarmed" into blaming Clark by May's officials, a charge that he will be forced to answer today.

So long as Whiteman sticks to his story, May's position should be secure. But the pressure on the Home Secretary is still rising. Leaked emails from the UK Border Agency suggest that thousand of passengers arriving on private jets were allowed into the country without any passport checks. All of which suggests that May has even more questions to answer than we thought.