The partygate inquisitor objected to the PM vetoing Scotland’s new trans law, which made it easier for over 16s to change their sex on their birth certificate.

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The legal change sparked a furious political row, with womens rights campaigners warning it would mean biologically male prisoners in female prisons.

And in a fresh controversy, government insiders now claim Ms Gray actively tried to kill off the plan behind the scenes in late December.

A source said she directly contacted political advisers behind the backs of ministers to lobby against the move – known as triggering Section 35.

At the time the row was a major embarrassment for Labour because their Scottish politicians had backed the Gender Recognition Act.

Ms Gray was in cloak and dagger talks with Labour to become Sir Keir Starmer’s chief of staff at the time.

A Government insider said: “We know the use of Section 35 embarrassed Sir Keir Starmer by highlighting Scottish Labour’s support of putting men in women’s prisons.

“Given Sue had already lined up her Labour job, was she already working for him in the heart of Government and seeking to save his blushes?”

Ms Gray’s move to work for Sir Keir is on hold while it is probed by Whitehall appointments watchdog ACOBA.

They are meeting over the next week and are expected to make their decision within the next month.

She could be barred from taking up her new job until after the next election.

Ms Gray declined to comment