The Cabinet secretary has told MPs that Britain went to war against Iraq on the advice of a one page legal document from the attorney general Lord Goldsmith.

The admission from Sir Andrew Turnbull brought a shocked response from politicians of all parties.

Labour backbenchers who opposed the war said the disclosure amounted to "gross maladministration" by the government.

The Tory shadow home secretary, David Davis, said the disclosure was "another example of Blair's government by whim". 

The revelation came after questioning by Tony Wright, Labour chairman of the Commons public administration committee and Gordon Prentice, a Labour backbencher.

Turnbull said Lord Goldsmith had presented his conclusions to the Cabinet which had been summarised in a parliamentary answer.

And finally he conceded: "There is not a longer version of that advice. This is the definitive statement of his views."