Four Yorkshire cities may have Mayors imposed by May 2012

Ministers have revealed they plan to introduce legislation for 12 of England's biggest cities – including Leeds, Bradford, Sheffield and Wakefield – to have Mayors installed in May 2012.

But despite the Conservatives having promised that voters would be able to veto the plans in a referendum, there are growing concerns Ministers may introduce them first and let voters deliver their judgment later.

Local government insiders suspect council leaders could even be given the title of Mayor first and given a run in office before a "confirmatory" referendum and election are held.

MPs and council leaders are warning Ministers against any such moves, which risk making a mockery of the Tory policy of giving people more say in how their local area is run.

However, last night officials in the department of Secretary of State for Communities and Local Government Eric Pickles refused to offer any guarantee of a referendum taking place before the first office holder is installed.

Clive Betts, Labour MP for Sheffield South East and chairman of the Commons Local Government Select Committee, said: "This seems another half-thought-through idea.

"You can't change the whole way we elect local representatives without first getting the consent of voters – it would be a nonsense to do that and then seek consent afterwards."

Elected Mayors were first introduced under Tony Blair but the initiative has had mixed success. In Doncaster, successive Mayors have hit trouble, and Labour was embarrassed by the electoral success of football club mascot H'Angus the Monkey in Hartlepool, in 2002, who was voted in after pledging free bananas for schoolchildren.

But the creation of a London Mayor is widely regarded as a great success, and buoyed by Boris Johnson's victory in 2008, the Tories unveiled a policy paper last year which pledged to hold referendums in the 12 biggest cities, adding: "In these cities, a mayoral system will be established unless voters reject that change." The Tory manifesto pledged to give citizens in those cities "the chance of having an elected Mayor".

But there has been a change of tone since the election, with the coalition agreement pledging to create directly elected Mayors in those cities "subject to confirmatory referendums and full scrutiny by elected councillors". The reference only to a "confirmatory referendum" has led to fears approval would only be sought after the change had already taken place.

While holding a referendum first would be the most open approach, it risks embarrassment if voters reject the idea and would also pit coalition Ministers against local leaders from their own parties, many of whom are sceptical about Mayors.

Sheffield City Council's Liberal Democrat leader Paul Scriven said: "If I were to become a Mayor tomorrow it doesn't change one jot the way I would work and lead for the city. I think it's an unnecessary distraction, and putting the power into one person's hands I feel is not necessarily the right way to go."

A DCLG spokesman refused to rule out the idea of a referendum after the post is created, saying: "We will be publishing more detail in due course."