Lawyers for Ciaran McClean (pictured) issued an application for judicial review of the agreement, claiming it will frustrate the peace process.

The move follows a crowdfunding appeal which raised £20,000 for the legal action. Mr McClean has now raised in excess of £50,000 towards his target of £100,000.

His claim states that the any agreement between the government and the DUP will breach the Good Friday Agreement as the government undertook to exercise power in Northern Ireland “with rigorous impartiality on behalf of all the people in the diversity of their identities and traditions”.

Critics say the deal infringes the government’s policy of neutrality and claim the deal also breaches the Bribery Act 2010 as it saw an extra £1 billion in funding for Northern Ireland.

Mr McClean said: “Following the success of the crowdfunding, I instructed my lawyers to issue the application for judicial review of the decision by Theresa May to enter into the agreement with the DUP.

“That agreement is, in my view, no more and no less than the purchase by the government of votes in Parliament using public money.

“It is clear to me and the thousands who have contributed to the crowdfunding on CrowdJustice that that is simply wrong and puts the Good Friday Agreement in severe danger.

“My lawyers have corresponded with the government and the response from the government offered nothing to dissuade us from pursuing this application.”