Britain went to war on the basis of a single piece of paper setting out the legality of invading Iraq, the country's most senior civil servant has revealed. The Government's case for war appeared to be in tatters last night after the Cabinet Secretary admitted that a parliamentary answer from Lord Goldsmith, the Attorney General, was the final legal opinion on the case for war. In an astonishing admission, Sir Andrew Turnbull disclosed that no "full" legal advice on an invasion of Iraq has ever existed. He confirmed that a short parliamentary answer by the Attorney General was the "definitive advice" on the war sent to the Prime Minister and that "there is no other version". The renewed doubts over the legality of the conflict are a severe setback to Tony Blair, who was hoping that Iraq would fade as a general election issue.