The FDA trade union’s legal challenge over the Government’s Safety of Rwanda Act is set to be heard at the High Court.

The trade union, which represents senior civil servants, previously said it was bringing legal action over the relationship of the Civil Service Code with the Government’s Safety of Rwanda Act.

The claim against the Cabinet Office is due to be heard on Thursday at the Royal Courts of Justice in London.

The FDA’s challenge concerns guidance from the Cabinet Office to civil servants which says they will be acting in line with the Civil Service Code if they follow a minster’s decision to remove asylum seekers to Rwanda, even if a Rule 39 measure has been made.

A Rule 39 interim measure from the European Court of Human Rights – branded a “pyjama injunction” because it can be issued outside normal court hours – contributed to the grounding in 2022 of the first flight that was set to carry asylum seekers to Rwanda.

In an order last month, Mr Justice Chamberlain said: “The claimant says that this guidance is wrong in law and that civil servants would be acting contrary to the code, as presently drafted, and therefore contrary to their terms and conditions of employment, if they acted contrary to such an interim measure.”

No decision on the legal challenge is expected to be made at Thursday’s hearing, which is due to begin at 10.30am.

The hearing comes after the Government told the court in a different case that it now plans to begin removals to Rwanda in late July.

At the start of a hearing on Monday in a challenge brought by charity Asylum Aid, the court heard the first flight is now planned for July 24.