Mr McClean, who pursued the legal action as a private individual and not in conjunction with the Green Party, claimed the agreement breached the Bribery Act 2010 and described it as a "corrupt bargain".

During the hearing, his lawyer tried to persuade the two judges that he had an "arguable" case, which should be given a full airing in court at a later date.

Dominic Chambers QC told them that under the June 26 agreement the Government had "purchased" the political support of the DUP for £1 billion, "and that sum will come from public money".

He argued the agreement was made for an "unlawful purpose", and said that it was "on its face unlawful because it makes provision for the expenditure of public funds for party political advantage".

The application was contested by two defendants, the First Secretary of State and the Attorney General.

Their QC, James Eadie, submitted in written argument before the judges that the criminal law of bribery "plainly does not apply to a confidence and supply agreement between political parties".

He stated: "The allegation that the agreement entails public expenditure which is unlawful at common law and/or without parliamentary authority is misconceived in particular because the expenditure contemplated by the agreement will have appropriate parliamentary authorisation."

The parliamentary deal - branded "shabby and reckless" by Labour - saw the DUP's 10 MPs agree to support the Conservatives' minority government in a series of key Westminster votes.

In exchange, Northern Ireland's largest party secured £1 billion of new Treasury investment in the region.

Under the "confidence and supply" arrangement intended to last until 2022, the DUP guaranteed that its MPs will vote with the Government on the Queen's Speech, the Budget, and legislation relating to Brexit and national security.

The DUP has insisted the Westminster arrangement will provide stability for the UK at a time of uncertainty while offering much-needed investment for the whole of Northern Ireland.

Belfast Telegraph