AN investigation was believed to be under way in Whitehall last night after a string of secret documents linked to today's British budget were leaked to the Daily Mirror newspaper.
Civil servants across Whitehall departments are likely to be grilled over the leak, which is unprecedented in modern times and will have sparked concern at the highest levels of government.
The Daily Mirror said it would not be publishing details contained in the highly sensitive dossier. But Downing Street declined to comment, or even to confirm whether the documents were genuine.
The 36 Whitehall documents, running to almost 100 pages, revealed changes in a wide range of taxes, according to the newspaper.
But the Mirror editor, Mr Piers Morgan, said last night that the paper had decided to hand the dossier back to 11 Downing Street. "Although we wouldn't normally hesitate to embarrass the government with such an amazing scoop, on this occasion we had a public duty to return such sensitive economic documents".
"Publication of so much detail from the Budget before the Chancellor's speech could have forced the stock market to close and cause chaos in the international money markets," Mr Morgan said in a statement.
Downing Street had confirmed to the newspaper that the documents were genuine, the Mirror said. Mr Morgan called the prime minister's office at 7 p.m. yesterday to reveal that his newspaper had the dossier.
He said most of the documents were press releases which would have been issued at the end of the Chancellor's speech to explain the announcements.
He declined to go into details about who had leaked the documents or whether they had been faxed over. But he added: "I think it would be fairly obvious why they chose the Mirror. If you were going to embarrass the government we are a perfect receptacle. And if anybody else out there has sensitive government documents we are in the market."
Of the 36 documents, 33 were from the Inland Revenue, two from Customs and Excise and one from the Scottish Office.
The documents are said to have included details of personal tax action - arguably the most sensitive subject in today's budget.
The Labour frontbencher, Mr Brian Wilson, said last night: "How can anyone trust Kenneth Clarke to run the economy when he loses half his Budget? This is just another reflection of the shambles which at present passes for government.
Mr Malcolm Bruce, Liberal Democrat Treasury spokesman, described the leak as "extremely serious". He added: "It does imply there will be tax cuts and other tax changes."
Such a leak is unprecedented in modern times, although just after the second World War Mr Hugh Dalton leaked parts of his 1947 budget to a reporter.