A crowdfunded legal challenge to the government's £1bn deal with the DUP reaches the High Court in London today, with the claimant arguing it breaches bribery laws.
Mental health worker and Northern Irish Green Party member Ciaran McClean will ask judges today to grant him permission to bring a judicial review over the legality of the deal.
McClean, who has raised almost £95,000 to fund the challenge, said: "For Thursday the battle lines are drawn. We say that the Tory/DUP agreement is in breach of the Bribery Act 2010 and breaches the standards for public spending obligations set by the Court in the Westminster corruption case Porter v McGill.
"In short the Government say this is a matter for Parliament and not the Courts under Parliamentary privilege. We say in response that Parliamentary Privilege cannot save this corrupt bargain and even if it could it would need a specific vote of Parliament on the deal to sanction it
The controversial deal was hastily struck by Theresa May in the morning after the election, as the extent of her disastrous campaign became clear.
The confidence and supply arrangement is less formal than a coalition agreement, but guarantees the government the support of the DUP's 10 seats in key votes, such as the Budget and the Queen's Speech.
But McClean claims it is "straight bribery - money for votes".
"The deal flies in the face of the Good Friday Agreement, under which the Government is obligated to exercise its power with 'rigorous impartiality' on behalf of all the people in the diversity of their identities and traditions," he added. "The Government is threatening hard won peace with their pact with the reactionary DUP."