Dominic Cummings has been named as a respondent in a sex discrimination case brought by Sonia Khan, whom he fired in humiliating circumstances as a special adviser to the former chancellor Sajid Javid.

Government solicitors tried but failed to remove Cumming’s name from a case brought by 28-year-old Sonia before an employment tribal in London.

It will add to the pressure on Cummings to step down as Boris Johnson’s most senior political adviser at 10, Downing Street, should he lose the case.

Sonia’s sacking took place in September last year in a blaze of publicity when she was escorted out of Downing Street by an armed policeman on the orders of Cummings.

He had accused her of being in touch with people close to Philip Hammond, who had been chancellor under Theresa May but was considered as being hostile to Boris on a range of issues, including Brexit.

Sonia, who had once been a special adviser to Hammond, had been taken on by Javid but he was not consulted when she was sacked. This was regarded as high-handed behaviour by Cummings but although Javid was livid at the dismissal of his aide, the chancellor did not force a showdown with Boris’s right-hand man.

In February Javid chose to resign as chancellor when Cummings ruled that all special advisers in 10 Downing Street, and at the treasury would have to be part of one team under his personal control.

Sonia denied inappropriate contact with any of the Hammond team but she was fired anyway by Cummings who demanded she hand over both her office and personal mobile phones to him.

In a meeting days after Sonia’s departure with Boris’s team of special advisers — known as “spads” — Cummings is said to have remarked with characteristic arrogance: “If you don’t like how I run things, there’s the door.”

The Guardian, which revealed Cummings had made a trip to his father’s home in Durham when he was in lockdown in London, has now disclosed his name remains as a respondent in the case filed by Sonia before an employment tribunal.

The paper reported on Tuesday that government lawyers had tried to remove Cummings’ name from the case. “The demand was rejected after barristers for Sonia Khan, the former chancellor’s media adviser who was marched by armed police from Downing Street, successfully argued that the behaviour of Boris Johnson’s chief aide was pivotal to the case.

“The disclosure will be seen as an attempt by the government to protect Cummings from further controversy.

“At an employment tribunal hearing in central London, a judge set the case for a five-day hearing in December at which the relationship between Cummings and Johnson will be scrutinised.

“Counsel for Khan, who is being backed by the FDA union (representing civil service workers), argued that Cummings was pivotal to the case and that what he had done personally, rather than just as an agent of the employer, was actionable. He is expected to be summoned as a witness. The hearing ruled that the cabinet office could be added as a respondent but Cummings would also remain.”

Bruce Carr QC, a former government adviser on employment law, said the naming of an individual as a respondent could mean he could be personally liable for damages.

“There are plenty of cases where it is appropriate and legitimate to include an individual as a respondent where that individual is central to the allegations of discrimination,” he said.

Watchdog slams government

Britain’s statistics watchdog chided the government on Tuesday for publishing data on coronavirus tests that it said were “far from complete and comprehensible”.

“The aim seems to be to show the largest possible number of tests, even at the expense of understanding,” David Norgrove, the head of the UK Statistics Authority (UKSA), wrote in a letter to health secretary Matt Hancock.

Criticism from the independent UKSA is likely to add to questions surrounding the government's handling of a pandemic that has killed almost 50,000 people in the United Kingdom.

“The secretary of state (of health) has spoken to Sir David and reiterated his department's commitment to continuing to work closely with the UK Statistics Authority to address their concerns,” a spokesman for Johnson said.

Concerns over the test data first came to light when the government set itself an ambitious target to carry out 100,000 tests per day by the end of April — a goal it said it met. But in doing so, it included in its figures tests mailed out to people but not necessarily completed.