Tony Blair has arrived back in Washington with an important message for the Obama team. The search for peace in the Middle East must be a priority for the new administration. The terrain is difficult but not impossible. The end of the Bush era offers real opportunities for this benighted region.

Mr Blair is right. He made his case before the Council on Foreign Relations in Washington articulately and passionately. He knows all the key players involved and is familiar with the issues. He seems genuinely devoted to the cause. He brings to the table his success in conflict resolution from Northern Ireland.

But Mr Blair is no longer the right man for the job. He should share the wealth of his knowledge with the incoming Obama foreign affairs chiefs and bow out gracefully.

A new era in the Middle East may or may not be about to unfold but it has a better chance of success without Mr Blair in the key role as envoy for the Quartet, the leading diplomatic group comprising America, Russia, the European Union and the United Nations.

I first met Tony Blair in Jerusalem more than 15 years ago at the home of Afif Safieh, now the Palestinian envoy to Moscow. He was there on holiday with his wife, both of them clearly fascinated by the seductive combination of politics and religion that is the city's lifeblood. At the time he was not even leader of the Labour Party. Neither of us imagined what impact he would one day have on the region.

Certainly in Arab eyes, Mr Blair is associated with a series of disastrous policy decisions. He will forever be remembered as the junior partner in the US-led invasion of Iraq. While America has managed to salvage something from the war, with the military surge and a change in tactics, Britain's reputation as a military power and experienced player in the region will take a long time to recover.

Then there was Lebanon in 2006. Blair backed the Israeli offensive against Hezbollah, even after it was clear that the campaign was misdirected, that innocent Lebanese were caught up in the attack, that huge damage was being done to the country's infrastructure and that one of the few democratically elected Western-leaning governments in the Arab world was being undermined.

Partly as a result of his support for the war, Mr Blair resigned last year and dedicated his work to finding peace in the region, a laudable ambition. But what does he have to show for 18 months on the sharp end of diplomacy? Some progress has been recorded in Jenin and Bethlehem, two West Bank towns where the Palestinians are taking on more responsibility. But little success has been made in persuading Israel to dismantle its checkpoints in the West Bank, a key factor in reviving the Palestinian economy.

The expansion of Jewish settlements in the West Bank has continued uninterrupted. The situation in Gaza has steadily deteriorated. The coastal strip remains under Hamas control and now threatens to become a humanitarian emergency. Benjamin Netanyahu, the Israeli right-wing opposition leader, is tipped to win elections scheduled for February with a far less compromising stand on talks with the Arabs. The joke in the region is that the only real beneficiary of Mr Blair's recent engagement with the Middle East is the American Colony Hotel in Jerusalem, where he has established his offices.

In spite of all the setbacks, Mr Blair until very recently kept up the Bush Administration's mantra that a final peace deal is possible by the end of 2008, when we were told a Palestinian state would be in place. This was either a delusion or an outright falsehood.

There was never any chance of this happening, despite the grand declarations at the peace conference in Annapolis more than a year ago. Similarly, the timetable for peace set out under the “road map” was nonsense. Mr Bush was never prepared to do the heavy lifting required to make peace in the region, or to engage key states such as Syria and Iran. Mr Blair shares some responsibility for this failure. His reputation in the Arab world is permanently tarnished.

Finally, there are serious questions about how much time and effort Mr Blair is prepared to devote to this issue. We are told that he has taken a job teaching at Yale University, is writing a book to be published next year, is a banking consultant and is actively promoting inter-faith dialogue, the environment, sports, and development in Africa. There are also strong hints that if a European presidency is ever created, Mr Blair would be first in line for the job.

The search for peace in the Middle East is not a part-time assignment. It requires full-time commitment, preferably by someone who has the right connections in Washington and the capitals of the region, but can also approach the work with fresh thinking and a clean slate.

Achieving peace in the Middle East has long been regarded as the Holy Grail of international diplomacy. Unfortunately for Mr Blair, it is beyond his grasp.

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