Former Birmingham Erdington MP Sion Simon, who left the Commons in 2010 to pursue his ambition of becoming mayor of the city, explains why he believes sitting MPs should also be allowed to apply to become Labour’s mayoral candidate.

I announced in February 2010 that I was resigning as a Government Minister and would be stepping down as MP for Erdington at the General Election, in order to campaign for an elected mayor for Birmingham.

At the time, people were shocked. They couldn’t believe I would give up a safe Labour seat and a Ministerial career in order to do seek a job that might never exist.

Two years and two months later, there are three former Ministers vying just to be the Labour candidate.

This is unprecedented in British history. It is indicative of a huge shift in the structure and location of power in England which will happen, gradually, over the next decade.

The move to elected mayors needs to be understood as only the beginning of a process the final scale of which will be bigger than the initial bang.

Such has become the potential stampede since my announcement that there is now a prospect of perhaps a dozen by-elections.

In Birmingham alone, the other two potential Labour candidates (Gisela Stuart and Liam Byrne) are sitting MPs. If either were selected, it would cause a by-election.

By-elections can cost hundreds of thousands of pounds and are a huge diversion of party activist and staff time and energy.

So the prospect of a dozen all over the country is making Labour high command nervous. Talk has been widely reported of disbarring sitting MPs from standing.

Which is what should have been done in the first place. I stood down from Parliament because I didn’t want to cause the party the expense and uncertainty of a by-election, and because I would not break the bond of trust with people who elected me to serve a full term.

I also thought it quite likely that the party, for those reasons, would rule sitting MPs ineligible for the Labour nomination.

But they didn’t, and now it is too late. If Labour MPs were now prevented, only a few weeks before the selection process begins, from seeking mayoral nominations, our enemies would use it against us. And we would deprive ourselves of some good candidates.

Sitting Labour MPs should now be allowed to stand.

They should sign undertakings to abide by the result and not to run as independents if they lose, and perhaps also to repay to the Labour party and the Exchequer the cost of their by-elections if they win.

But they should be allowed to stand. Bring it on.