An argument regularly used to support the call for directly elected mayors is that whoever wins will thus have a mandate from the public to carry out their programme or manifesto. But as with so much of the bluster and sloganeering surrounding the mayoral debate, the reality is not so straightforward.

If Birmingham votes for a mayor in May’s referendum, November’s election would use the Supplementary Vote system. Under SV voters indicate a first and second preference. If no candidate secures 50% of the total votes cast, the top two candidates continue to a second round, with all other candidates eliminated. The second choice votes of those who voted for the eliminated candidates are then counted, with any cast for the top two candidates redistributed accordingly. The candidate who then has the most votes is declared the winner.

It can be expected that Labour, the Conservatives and the Liberal Democrats, as well as Respect, UKIP, the Green Party, and perhaps several fringe parties, will field candidates. A number of independents are also expected to stand. It is therefore probable that the eventual winner will have received considerably less than half of first preference votes (a figure of around 30-35% appears reasonable but in certain circumstances it could be lower), and they might even have finished second in the initial ballot.

Transferable voting systems are fine of themselves (and with most voting mechanisms the winning candidate or party receives under half of first preferences). In this instance the problem arises when there is a mayor with a somewhat less than equivocal mandate (and who may not even have won the popular vote), holding a post commanding extensive powers coupled with a low threshold of accountability.

There is a danger that such a mayor, wielding the authority to implement a multi-billion pound budget and key council policies while supported by as few as one-third of city councillors, could reduce both public confidence, and ultimately the desire for public participation, in our democratic institutions.

To grant one person such powers, the least we should expect is that they have an incontestable mandate. And that is very unlikely to be the case.