Three former Labour MPs and a Tory peer challenge a ruling that they are not protected from prosecution by parliamentary privilege over allegations that they fiddled their expenses.
The appeal by David Chaytor, Elliot Morley, Jim Devine and Lord Hanningfield will be heard by the Lord Chief Justice, Lord Judge, sitting in London with the Master of the Rolls Lord Neuberger and Sir Anthony May.
As a result of a decision earlier this month by Mr Justice Saunders, sitting at Southwark Crown Court in central London, the men - who all deny theft by false accounting - are facing crown court trials.
Mr Justice Saunders rejected argument that they were protected by parliamentary privilege and should be dealt with by Parliament alone. He granted the four leave to appeal. The judge said: "I can see no logical, practical or moral justification for a claim for expenses being covered by privilege; and I can see no legal justification for it either."
It was argued by the defendants that submitting an expenses form was part of the proceedings of Parliament, and therefore protected by parliamentary privilege.
Former Bury North MP Chaytor, 60, of Todmorden, Lancashire, is accused of falsely claiming rent on a London flat he owned, falsely filing invoices for IT work and renting a property from his mother, against regulations.
Ex-Scunthorpe MP Morley, 57, of Winterton, north Lincolnshire, is charged with falsely claiming £30,428 in interest payments between 2004 and 2007 towards a mortgage on his home which he had already paid off.
Devine, 57, of Bathgate, West Lothian, formerly MP for Livingston, is accused of wrongly submitting two invoices worth a total of £5,505 for services provided by Armstrong Printing. He faces a second charge alleging that he dishonestly claimed cleaning and maintenance costs of £3,240 by submitting false invoices from Tom O'Donnell Hygiene and Cleaning Services.
Former Essex County Council leader Lord Hanningfield, who is also known as Paul White, 69, of West Hanningfield, near Chelmsford, faces six charges of making dishonest claims for travelling allowances.
Each of the four defendants, who are all on unconditional bail, face separate criminal trials, pending the outcome of the appeal.