MPs' committee summons Campbell and his boss

Tony Blair and Alastair Campbell have been summoned to public hearings by a committee of MPs to answer questions on the intelligence used to justify war in Iraq.

Jack Straw, the Foreign Secretary, and John Scarlett, chairman of the Joint Intelligence Committee, have also been asked to give evidence to the influential Foreign Affairs Committee. Sir David Omand, permanent secretary at the Cabinet Office and the Government's security and intelligence co-ordinator, has been asked to attend.

Whitehall sources said Donald Anderson, Labour chairman of the committee, had written to the men asking them to appear during a week of back-to-back hearings later this month.

Mr Blair and Mr Campbell, the Prime Minister's director of communications and strategy, are expected to defy the committee's request to give evidence, despite warnings that a failure to do so would be an embarrassment to the Government. Mr Blair will face intense questioning on the affair next month, when he is scheduled to give evidence to the Liaison Committee.

The Foreign Affairs Committee, which is due to report next month, will focus on whether the Government "presented accurate and complete information to Parliament in the period leading up to military action in Iraq, particularly in relation to Iraq's weapons of mass destruction".

Members will meet on Tuesday to finalise plans for a week of public hearings from 16 June, which promise to maintain intense pressure on ministers. Mr Blair and his advisers have denied manipulating intelligence reports in the run-up to war.

Members of the Parliamentary Intelligence and Security Committee, which reports to the Prime Minister, are expected to reveal the terms of reference of their inquiry into the build-up to war on Tuesday.

The former foreign secretary Robin Cook increased the pressure on Mr Blair yesterday by warning that the Attorney General's opinion, which formed the legal basis for military action, would be undermined if no weapons of mass destruction were found in Iraq. In an interview to be screened on GMTV tomorrow he said: "Remember he said the war was legal because we needed to disarm Saddam Hussein.

"I think it's a very interesting question, but one for the lawyers, as to whether that opinion stands up if there were actually no weapons that needed to be disarmed."

Labour unease at the British use of intelligence increased when Hans Blix, the United Nations chief weapons inspector, launched a highly critical attack on the information given to him by Britain and America. Speaking on Radio 4's Today programme he accused both countries of "jumping to the conclusion" that weapons that were unaccounted for existed in Iraq. Mr Blix said: "Only in three of those cases did we find anything at all, and in none of these cases were there any weapons of mass destruction, and that shook me a bit, I must say. I thought, 'My God, if this is the best intelligence they have and we find nothing, what about the rest?'"

Doug Henderson, a former armed forces minister, said: "This is yet more opinion, very authoritative opinion, that the evidence that Britain and America used to assess the need to go to war in Iraq was thin. Dr Blix is probably the most important commentator yet on this."

Malcolm Savidge, Labour MP for Aberdeen North and an outspoken critic of the war, said Mr Blix's comments added to fears that the war had been started on false pretences. He said yesterday: "It makes it vital that there should be a thorough investigation of this both in Britain and the United States."