The head of the civil service has been asked to investigate whether the Home Secretary's advisers "may have been briefing against" the head of the UK Border Force over the relaxation of checks at ports during the summer.
The Labour MP Simon Danczuk has written to the Cabinet Secretary Sir Gus O'Donnell asking him to investigate whether Theresa May's staff may have broken the code of conduct for special advisers. The move followed a series of allegations in the media about Brodie Clark's actions before he resigned on Tuesday, saying his position had been made "untenable".
Mr Danczuk wrote: "I am writing to raise serious concerns about suggestions that advisers to the Home Secretary may have been briefing against a serving civil servant who had been suspended and therefore had no right to reply. A number of allegations about Brodie Clark, who had just been suspended as the head of the UK Border Force, appeared in newspapers over the weekend."
In the letter, which was also sent to Ms May, Mr Danczuk pointed to claims that officials had been instructed to refuse any offer of resignation by Mr Clark, as well as descriptions of him as a "rogue civil servant". The Rochdale MP went on: "If the information about Mr Clark, who at that time was still suspended and had not resigned, came from one of the Home Secretary's special advisers, then this appears to be a breach of the code [of conduct for special advisers]."
The code, published on the Cabinet Office website, states that "the preparation or dissemination of inappropriate material or personal attacks has no part to play in the job of being a special adviser as it has no part to play in the conduct of public life".
During the summer, to ease congestion at ports, the Home Secretary authorised a pilot scheme, allowing some checks on European travellers to be relaxed. But she told the Commons that Mr Clark went further, scaling back checks on non-EU nationals without her approval.
Theresa May has been sent a list of 14 questions the Homne Affairs Committee wants answered about events around Brodie Clark's treatment.