Boris Johnson is fuming about a police investigation into how he became the owner of a red leather cigar case that once belonged to Saddam Hussein's former deputy Tariq Aziz.
It is no secret that Mr Johnson removed the case as a souvenir from Mr Aziz's villa after US troops entered Baghdad in 2003. But now he has received a letter from the Metropolitan Police arts and antiques unit inviting him to give it back.
Mr Aziz has bigger things to worry about than the loss of a cigar case. Captured by US troops in April 2003, he has spent almost five years in prison without trial.
The police say stealing cultural artefacts from abroad is a serious matter. But Mr Johnson suspects a dirty trick by political opponents who want to damage his chance of unseating Ken Livingstone in the May election for London Mayor.
The Met was apparently alerted to the case in the past few days, although the Henley MP has had the cigar case for nearly five years, once covering himself with ash when he was showing it off to friends. The letter said: "Police attention has been drawn to reports suggesting you have in your possession an item that may be Iraqi cultural property, namely a cigar case from the address of Tariq Aziz." The letter suggested Mr Johnson should surrender the cigar case to Scotland Yard "for further investigation".
A promise to combat crime has been one of the central features of Mr Johnson's campaign. He has said the Met are "burdened by too much bureaucracy. Too much money is spent on form filling when it could be used to employ more police on the beat".
This particular police inquiry is based on evidence supplied by Mr Johnson himself, in a column he wrote for The Daily Telegraph in May 2003, describing a visit to Mr Aziz's wrecked, looted villa on the banks of the Tigris.
"I spotted something on the floor," he wrote. "It was a fine red leather cigar case, capable of holding three Winston Churchills. It was located in the front hall of the villa of Tariq Aziz, a known lover of cigars. And therefore, unless I missed my guess, it was the cigar case of Tariq Aziz. Instinctively, I reached down to snatch it up. This cigar case had attended the innermost meetings of the Ba'ath Revolutionary Council. If ever Saddam had given away the secret location of his weapons of mass destruction, the chances are that this cigar case was in the room. That is why I picked it up.
"He was a vain and conniving adjutant to terror, and I have temporarily taken his cigar case for safe keeping. Had I left it, the thing would of course have fallen into the hands of someone even more hostile to Tariq Aziz than me. If he wants it, I suppose he can have it back."
Mr Johnson reacted furiously to the investigation: "There were over 18,000 crimes in London last month and yet the police write to me about this. What this shows is a concerted effort by my political opponents to waste police time by dragging up an article that I wrote five years ago and trying to make political mileage out of it."
A Met spokesman said: "The Met works very closely with a number of countries, including Iraq, to recover items that are considered culturally significant. The Metropolitan Police Service treats the theft of, and cultural dealing of, property from abroad very seriously. The steps we are taking are proportionate with a view to repatriating an item which could be of cultural or historical significance."