The High Court will rule on the House of Commons' bid to overturn an information watchdog's decision to force disclosure of MPs' expenses.
The Commons challenged the Information Tribunal's demand that a detailed breakdown of MPs' additional costs allowances (ACA) must be provided under the Freedom of Information Act.
The Commons is also seeking to block the Tribunal's decision that MPs' addresses should be disclosed.
The allowances cover expenditure incurred when an MP is away from home on parliamentary duties, including the cost of running second homes and general household bills.
They have come under sustained criticism in recent months following the publication of the "John Lewis list" of household items MPs can purchase under their £23,000-a-year second homes allowance.
The list includes £10,000 kitchens and £6,000 bathrooms.
The legal challenge, expected to cost more than £100,000, was instigated by a Commons committee chaired by Speaker Michael Martin.
The ruling will be given by Sir Igor Judge (President of the Queen's Bench Division), Lord Justice Latham and Mr Justice Blake.
