Republican MPs criticised for taking taxpayers' money for London residences even though they do not take their seats at Westminster

Sinn Féin's five MPs each claimed £21,000 in second-home allowances from the UK parliament last year, despite refusing to take their seats in the House of Commons.

The republican movement said the money was paid for renting two houses in London used by Gerry Adams, Martin McGuinness, Michelle Gildernew, Pat Doherty and Conor Murphy when they are working in the capital.

Sinn Féin MPs have never been allowed to take their seats in the Commons because they refuse to swear an oath of allegiance to the Queen due to the fact that they do not recognise Westminster's authority over Northern Ireland. In 2001, as part of the Northern Ireland peace process, the government altered parliamentary rules to allow them access to Westminster allowances and office space despite not taking their seats. They are not allowed the MPs' salary of £64,766, however.

The details of the Sinn Féin arrangements were criticised yesterday by the Conservative spokesman on Northern Ireland, Owen Patterson. "It is completely unacceptable for Sinn Féin representatives, who won't even sit in parliament, to claim hundreds of thousands at the taxpayers' expense," he told the Daily Mail.

According to the latest figures, the party has claimed more than £400,000 on London properties since 2001-2. "This was agreed as part of the political negotiations eight or nine years ago," a Sinn Féin spokesman in Belfast told the Guardian last night.

"We were given the same allowances that other parties are entitled to. The MPs do not take the salaries. We rent two houses in London. We publish an audit of our expenses every year in Dublin."

Martin McGuinness, Conor Murphy, Michelle Gildernew and Pat Doherty all claimed £21,000 of a maximum £23,083 from the additional costs allowance in 2007-08, while Gerry Adams, the republican party's president, claimed £21,131.

A Sinn Féin spokesman said the party made no apology for refusing to sit in the House of Commons, nor for "ensuring that those people who vote for Sinn Féin get the same democratic entitlements as everyone else".

He added: "When Sinn Féin secured expenses from Westminster in line with our democratic mandate we made it clear that we would use the facilities and resources to on one hand provide a top-quality constituency service and on the other to campaign in England and amongst MPs for Irish unity and independence. This is exactly what we have done."

He said that all five MPs had been active "both in providing a top-class constituency service, including fully staffed offices, and in the United Ireland campaign, which will see a major conference in London in the coming year. This is what we are elected to do and what we will continue to be engaged in, in the time ahead."

Unionist parties were quick to criticise Sinn Féin. Tom Elliott, an Ulster Unionist member of the Stormont assembly, said: "It is staggering that MPs who refuse to represent their constituents in parliament are funded by the UK taxpayer to have houses in London. At a time when jobs are being lost and public spending is being squeezed, why exactly are UK taxpayers funding absentee Sinn Féin MPs? Why exactly are UK taxpayers paying for Sinn Féin MPs to have residences in London when Sinn Féin MPs do no work in parliament?

"It is essential that the review of MPs' salaries and expenses clearly links this money from taxpayers with MPs actually doing their job in parliament."

A spokesman for the Democratic Unionist party said: "The DUP uses any and all allowances we receive to serve the constituents we represent and to enable us to perform our parliamentary duties. It is for others to explain how they can take Westminster allowances without actually sitting in the House of Commons and representing their constituents."

According to Commons rules, the purpose of the additional costs allowance – known as the second-home allowance – is "to reimburse members for necessary costs incurred when staying overnight away from their main home for the purpose of performing parliamentary duties".

All MPs except those living in inner London can claim it so they can have a base near Westminster as well as one in their constituency.

There is no suggestion the Sinn Féin MPs have broken parliamentary rules in claiming the allowance.

Additional costs allowance claims by ministers Jacqui Smith, Tony McNulty, Alistair Darling and others have all been the source of controversy recently. Smith defended herself again yesterday for registering the house she shares with her sister in London as her main home and her family property in Redditch as her second home.

The committee on standards in public life is expected to conclude an inquiry into MPs' pay and allowances by autumn.