Jim Sheridan, MP for Paisley & Renfrewshire South, became the first parliamentary private secretary — the unpaid assistants to ministers who are one step away from ministerial rank — to go public with his concerns about the Middle East. He criticised the decision to allow American planes carrying bombs to Israel to refuel at Prestwick airport.

Other aides, including Ann Keen, Gordon Brown’s PPS, supported the growing calls for an immediate recall of Parliament to discuss the crisis, a move that ministers were resisting. However, there were growing signs that they will eventually agree to a special sitting early next month.

Mr Sheridan’s resignation is damaging to Mr Blair because he is seen as a loyalist and he backed the Iraq war. “The reason I am resigning is the current conflict in the Middle East and once again the Palestinian situation has been put on the back burner,” he told Sky News.

Mr Sheridan, 52, added: “I don’t expect my resignation will have any significant impact on the Prime Minister’s objectives in the Middle East, which I genuinely believe to be honourable on his part, but I don’t believe they reflect the core values of the Labour Party or indeed the country.”

He called for Mr Blair to adopt a stance closer to that of other European capitals.

The Times has learnt that ministers are reconciled to having to give way to demands for a September sitting of Parliament if the crisis in the Middle East does not subside. But they are firmly opposed to a swift recall.

John Prescott, on his first full day standing in for Mr Blair, discussed the growing pressure for a return with colleagues and officials. Afterwards his spokesman said that the issue would be kept under review.There is no desire within the Government or the Conservative leadership for an early recall while most ministers and opposition frontbenchers are away on their family holidays. The taxpayer would have to pick up the bill for bringing hundreds of MPs back. Ministers say there is little influence the Commons could wield in the present situation and MPs would face a public backlash.

By mid-afternoon yesterday, about 150 MPs had signed a letter to Jack Straw, the Commons Leader, demanding that Parliament be reconvened. More than a third were Labour MPs and virtually all the Liberal Democrats signed up. The organisers, the left-wing group Compass, claimed a coup with the addition of the name of Paddy Tipping, Mr Straw’s parliamentary aide, to the list. It was emphasised by insiders, however, that this was not a signal of Mr Straw’s support for an immediate return.

Mr Straw is understood to be in favour of a resumption of Commons sittings in September, which were introduced as an experiment in 2003 but have not been held in the past two years. In the letter to Mr Straw, the MPs said that allowing the United States to use British airports as staging posts on their way to deliver bombs to Israel had given the impression that Britain had assumed a “a tacitly active and less than impartial role in the conflict”.

Its signatories include several former Labour ministers, including John Denham, Clare Short and Michael Meacher.

They said it was “absolutely vital” that public concern over Israel’s military action, and Britain’s role, should be discussed. The failure to call for an immediate ceasefire “has cost many innocent lives and may continue to do so”. They also argued that because Mr Blair conceded that the crisis was of such a magnitude that he should delay his holiday, Parliament should also play its role.

Sir Menzies Campbell, the leader of the Liberal Democrats, said that given the worsening situation in the Middle East Parliament needed to be recalled as a matter of urgency.

Denis MacShane, the former Europe Minister, said: “MPs cannot wait until October to hear from the Prime Minister a full account of the crisis and to express the concern of our constituents about the continuing carnage.”

Kim Howells, a Foreign Office minister, said that he was not certain what bringing back Parliament would achieve. He added: “I’m sure Jack Straw will look at any demand very, very carefully. That’s what he’s there for.”

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