London Mayor Ken Livingstone has denied reporting Tory rival Boris Johnson to police over the alleged "illegal removal" of a cigar case from Iraq.

Johnson has blamed the Scotland Yard inquiry on a concerted effort by his political opponents and branded it a waste of police time.

Johnson admitted removing a red leather cigar case as a souvenir from Mr Aziz's villa after US troops entered Baghdad in 2003.

He has now received a letter from the Metropolitan Police arts and antiques unit inviting him to give it back.

The Livingstone campaign said it considers the issue "ridiculous".

Meanwhile, Johnson has opened up a clear lead over Livingstone in the race to become the next mayor of London, a poll has found.

The YouGov survey suggested 44 per cent intend to vote for Johnson, 39 per cent for current mayor Livingstone and 12 per cent for Lib Dem Brian Paddick.

The poll of more than 1,000 voters was conducted for ITV1's London Tonight.