That was the theory. In practice, there’s no escaping the fact that Mr Byrne effectively said he was ready to leave his Westminster friends behind and do something else, if the chance arose.

There’s nothing wrong with that, but one or two Labour figures at Westminster apparently seized the opportunity to get revenge on a colleague who sometimes espouses worrying “right-wing” or “Blairite” views, such as the idea that the welfare system should offer more help to people who have contributed to society, or that Labour must have more to say about public services than simply promising to spend more money.

Hence, Mr Byrne has lost his role as head of Labour’s policy review, although he remains in the shadow cabinet. The move was treated with glee by Labour activists who care more about ideological purity than winning elections and, indeed, by David Cameron.

Then we come to Gisela Stuart, another Labour mayoral hopeful, who will carry on as MP for Edgbaston.

If she stands for re-election, either in Edgbaston or in the new Harborne constituency likely to be created by boundary reviews, she will face charges – unfair as they may be – that she was ready to abandon her constituents to pursue other goals.

Rarely in politics has there been a tale of more woe than the battle to create a mayor of Birmingham and the MPs who hoped to wear the chains of office.