As an Irish republican I can only see this as being detrimental the welfare and well-being of the Irish people

Tommy McKearney Former republican prisoner

But they are now able to use the palace's facilities and receive office allowances after a controversial Commons vote, opposed by unionist parties and the Conservatives, last month.

Opponents say Sinn Fein has given no commitments in return for the privileges, but the government says the move will encourage Sinn Fein to become more integrated into the UK's democratic processes.

'Sour grapes'

Gerry Adams, Martin McGuinness, Pat Doherty and Michele Gildernew are flying to London to take up the office facilities available to all other MPs.

Mr McGuinness said even if the Commons oath was removed, Sinn Fein would refuse to take their seats in a parliament whose legitimacy they did not accept.

Speaking on BBC Radio 4, the Northern Ireland education minister accused opponents of the move of "sour grapes".

David Trimble: "Sinn Fein showing double standards by taking up offices"

"These are people who are refusing to recognise that we as elected MPs are entitled to what we are receiving today and we are going to use all of what we gain today in an appropriate fashion and in the interests of our constituents."

The offices - one each for Mr Adams and Mr McGuinness and a shared office for the others - are near the Commons chamber in one of the most sought after locations by MPs.

It is understood a fourth office will be made available to Sinn Fein in March.

'Propaganda coup'

Shadow Northern Ireland secretary Quentin Davies renewed Tory criticism of the decision on Monday.

Mr Davies said it gave Sinn Fein a "great propaganda coup" which would add to the agonies already felt by the families of IRA victims.

John Reid has said will encourage Sinn Fein into democratic process

"I'm afraid it will be displayed as the British government licking their boots," added the Tory MP.

The Tories, like Ulster Unionist and Democratic Unionist MPs, say Sinn Fein was getting a London propaganda and lobbying office at taxpayers' expense, without giving any commitments in return.

But Northern Ireland Secretary John Reid said in December that he believed Sinn Fein's MPs would eventually take their seats in the house following the lifting of the ban.

Ulster Unionist leader and Northern Ireland First Minister David Trimble made the same prediction at the weekend, but he accused the republican party of misleading its supporters about its commitment to a united Ireland.

Grassroots worries

"It will be interesting to see what explanation Sinn Fein will give as to how walking into Westminster is a step towards a united Ireland when it very obviously is a step in the opposite direction," he told BBC News.

Sinn Fein's move into Westminster comes after a party meeting in County Meath at the weekend.

Party leaders heard concerns from the republican grassroots about the IRA's disarmament move last October and the perceived lack of response from the British Government and the unionist community.

Mr Adams and Mr McGuinness are due to meet Tony Blair at Downing Street later on Monday to raise the republican community's growing unease about the government's response to recent loyalist paramilitary murders and attacks.

'First step'

Former republican prisoner and hunger striker Tommy McKearney said there was much scepticism about the move among Sinn Fein members.

"It is undoubtedly the first step in the Sinn Fein party taking full membership of the House of Commons and entering the floor of the House of Commons," he told BBC News.

"As an Irish republican I can only see this as being detrimental the welfare and well-being of the Irish people."