Brodie Clark, the UK Border Force official who resigned following revelations that passports weren't checked properly at UK ports and airports over the summer, has denied he is a "rogue officer".
Facing MPs on the Home Affairs Select Committee, he said: "Nothing could be further from the truth".
Clark has been called to give his side of the story which has brought immense pressure on the home secretary Theresa May, who insists that UK Border officials relaxed the checking of passports far beyond the terms agreed by ministers, as part of a pilot scheme introduced earlier this year.
The Home Office says that while ministers agreed to a limited relaxation of passport checks for some passengers, officials then went much further than agreed, and ignored a veto by the Home Secretary on whether the pilot scheme should be extended.
Clark was suspended two weeks ago in connection with the revelations.
He then resigned a few days later, and in his resignation statement suggested he'd been made into a political scapegoat.
Clark's evidence on Tuesday morning contradicted the home secretary's account - and he called May a liar in all but name.