Edwin Coe has launched an official legal challenge against a possible confidence and supply agreement between the Conservatives and the Democratic Unionist Party (DUP) on the grounds it could jeopardise the Good Friday agreement.

David Greene, head of litigation and dispute resolution at Edwin Coe LLP, will act for Ciaran McClean, a Green party politician in Northern Ireland who is the lead claimant in the case.

Greene said his team had sent a letter of action to the Government in which they ask it to rethink its plans to form a deal with the DUP. He said the firm had given the Government seven days to respond its assertions before it would begin proceedings.

The matter is the second legal challenge Greene has mounted against the Government in the course of a year.

Last year, Greene acted for Deir Dos Santos, one of the claimants responsible for taking the Article 50 case to the Supreme Court, in which the judges ruled that parliament must have a vote on process of exiting the European Union.

He acted alongside partners at Mishcon de Reya who represented the lead claimant in the case, Gina Miller. Between them they were successful in convincing judges that Parliament was sovereign and that the formal process of leaving the EU could not be triggered by royal prerogative alone.

Greene told The Lawyer:  “The decision to enter into an agreement with the DUP is in breach of the Good Friday agreement, and in particular Article 1 which does not just require impartiality, but rigorous impartiality. The Government relying on the DUP is in our view in breach of that requirement.

He continued: “Rigorous impartiality expressly requires independence and we do not believe the Conservatives will be independent as required by the Good Friday Agreement. There is a legitimate expectation on behalf of the citizens of  Northern Ireland that the government should not only be rigorously impartial, but appear to be rigorously impartial.”

Green will be acting alongside associates Dominic de Bono and Zahira Hussain. If the proceedings go ahead, they will instruct Maitland Chambers’ Dominic Chambers QC and John Cooper QC at 25 Bedford Row.

It is thought the government will bring in the Attorney General Jeremy Wright and James Eadie QC of Blackstone Chambers for its legal representation.