Mike Whitby could have an 18-month stint as Conservative mayor of Birmingham without ever having been elected to the powerful position.
He is guaranteed to retain power even if Labour wins a majority of seats on the city council.
A clause in the Localism Bill raises the prospect of a political stalemate if Labour takes control of the council chamber at the 2012 elections.
Coun Whitby is certain to be appointed shadow mayor at the end of this year when the bill becomes law.
He will have all the powers of a directly elected mayor to choose a cabinet and take executive decisions.
A referendum asking people whether they want to be governed by a mayor will be held in May 2012, at the same time as the council elections.
If the poll delivers a ‘yes’ vote, Coun Whitby will remain shadow mayor until a mayoral election is held in 2013.
Last year the Government hinted that, if the Tory-Lib Dem coalition running Birmingham was to lose control of the council in 2012, the shadow mayor position would pass from Coun Whitby to Labour councillor Sir Albert Bore as leader of the majority group.
But the Localism Bill dealing with mayoral elections in 10 English cities, including Birmingham, makes it clear this is not now the case.
It states that a shadow mayor must stand down only if the referendum delivers a ‘no’ vote, or if he is not successful at a council’s first mayoral election.
The decision could make life difficult for Coun Whitby, who would face the tricky task of pushing through the city’s 2012-13 budget if the Tory-Lib Dem coalition he currently heads does not have a majority in the council chamber.
Under rules for the mayoral system, the 120 city councillors retain the right to set an annual budget and pass the Council Plan, setting out a broad framework of policies.
The prospect of Coun Whitby enjoying a year and a half as mayor would also make it difficult for the Conservative Party to select an alternative candidate for the 2013 mayoral election, Sir Albert claimed.
Sir Albert warned that Coun Whitby’s elevation to city mayor would be viewed as “profoundly undemocratic”, since the council leader has spoken out many times against the principle of elected mayors and would inherit the position in Birmingham without ever facing the electorate.
He accused the Government of attempting to shore up Tory-Lib Dem control of the council “through whatever means possible”.
Sir Albert (Lab Ladywood) added: “This is a nonsense and untenable. I don’t think the people of Birmingham will take kindly to the fix that is being suggested.”
He is urging the Government to think again, and warned of the “nightmare scenario” that he said would unfold if Birmingham had a Conservative mayor attempting to run a council with a clear Labour majority.
Sir Albert said it was wrong for a council leader, from any political party, to be appointed shadow mayor. The position should not be filled until a mayoral election can be organised, as soon as possible after the referendum, he added.
Since elected mayors outside of London were introduced 10 years ago, several councils have experienced political difficulties.
Independent mayors in Doncaster and Middlesbrough are among those who found their budgets rejected.
But there have been no examples of mayors from mainstream political parties having to deal with a council chamber where the majority of members are from a rival party.