The Tories have claimed that Downing Street used President Bush to put pressure on the Conservative Party to support Tony Blair's stance on Iraq.

Alastair Campbell told the prime minister in a letter marked "restricted-personal" that ministers should use the threat of being punished by the Bush administration to keep the pressure on the Tories to support the government.

On the eve of a Commons debate on Iraq in June last year, Campbell wrote: "The final judgment to make, dependent on what the Tories agree today, is how hard to hit them for opportunism if they break ranks or, as is more likely, if they diddle.

"They need to know there will be a Bush price to pay on that."

The letter was presented to the Hutton inquiry last year.