Tony Blair is today expected to announce an inquiry into the intelligence on which he based his decision to go to war with Iraq.

Some form of announcement had been expected last night after it became clear he would have to bow to pressure to tackle the question of why no weapons of mass destruction have been found.

But Downing Street said the Commons Speaker had decided it would be "more appropriate" for Mr Blair to spell out how the failure to uncover Iraqi WMD would be addressed during his appearance this morning before the Commons liaison committee.

The Prime Minister will be questioned for two hours by a panel made up of the chairmen of various select committees.

A No 10 spokesman declined to say what Mr Blair would announce.

Both the Tories and the Liberal Democrats insisted there should be a fully independent inquiry into the intelligence which appears to have been so badly wrong it led Mr Blair publicly to claim for months that Saddam had WMD.

Mr Blair's official spokesman said last night: "The Prime Minister believes that the war was justified and remains justified."

However, he conceded it was "a fact of life whether we like it or not" that questions were being asked about why no WMD has been uncovered by the coalition's Iraq Survey Group (ISG).

There were now valid questions about that, said the spokesman, adding: "It's valid to find a mechanism to try to address that question."

Mr Blair has been refusing for months to hold such an inquiry, urging people to wait for the outcome of the ISG's work.

But that position became untenable after US President George Bush announced he was asking an independent commission to explain the difference between what intelligence material said the allies could expect to find in Iraq, and what has been discovered.

Mr Bush said he would consult the former head of the ISG, David Kay, about the work of his commission. Mr Kay told Congress last week that "it turns out we were all wrong, probably" about the threat posed by Iraq.

Foreign Secretary Jack Straw was asked last night what lay behind the Government's apparent change of heart on the inquiry issue.

He confirmed that the Government was "actively considering an announcement".

Mr Straw told journalists the Government had been facing two issues. The first was whether it had told any untruths about the nature of the intelligence it had received and relayed to the British people.

He said that Lord Hutton's report had "dealt conclusively" with that issue.

The second issue was whether the intelligence received by the Government was reliable.

Mr Straw said: "We understand, of course, that there have been questions about the second issue, and they have been raised by Dr Kay's remarks, and the stage reached by the Iraq Survey Group.

"It is taking account of these factors that lies behind decisions which we are likely to announce later on."'

Tory leader Michel Howard said: "Everybody now recognises that something went wrong over the intelligence."

Liberal Democrat leader Charles Kennedy said: "At last the Prime Minister has acknowledged that it is essential to address the unanswered questions raised by the continuing absence of weapons of mass destruction in Iraq."

Labour chairman of the Foreign Affairs Committee Donald Anderson said an inquiry was needed to "re-establish trust in our intelligence community".

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