Oh for heaven’s sake, here we go again.

The Sheffield City Region, like Manchester before it, has just signed a devolution agreement. The region, a collection of nine local authorities in South Yorkshire, Derbyshire and Nottinghamshire, will be given significant extra power over strategic planning and transport budgets, to the tune of £30m a year.

In exchange, as chancellor George Osborne has been making clear ever since he got the devolution bug, all it had to do was agree to elect a “metro mayor”. The first election will be in 2017.

Osborne, whatever his flaws, is doing more to decentralise power in this country than anyone since the early Blair years. More than that, he’s devolving powers to areas that are extremely unlikely to elect Tory mayors.

So how do you think the left is reacting?

We’ve been here before. Exactly the same complaints were made when Greater Manchester agreed to a mayor; and the arguments were exactly as flawed.

The population of Sheffield City Region never rejected a mayor. The population of the city of Sheffield did, but that’s just one of the region’s nine authorities. Let’s see the numbers in pie chart form:

 

Or, if we wanted to boil this down to its simplest form:

At a fringe event at Labour conference on Tuesday, Jon Trickett, the shadow communities secretary, advised a roomful of council leaders not to trust Osborne’s offer of devolution. It would only lead to disappointment. If they wanted real influence, he implied, they should wait for the next Labour government.

There are three problems with that. One is that Labour is, charitably, divided on devolution: there are many in the party who simply don’t believe in it, because they think it’ll make it harder to redistribute wealth.

Another is that, even if the party were committed now, there’s no guarantee it would be by the time it got to power. It’s easy to pledge to give away power in opposition; much harder to actually do so once you have it in your hands.

But the big one is this: Labour is so far from government right now they might as well be promising council leaders a unicorn egg if they wait. It’s an utterly meaningless promise.

There’s a clash of interests, here. Labour’s national leadership doesn’t want to be seen to support a Tory policy; Labour’s local leadership want more powers, on the grounds that if budget cuts are inevitable, they are least might as well get some extra power too. Those two groups are now on opposite sides of this debate.

Almost as if that’s what Osborne has been trying to achieve all along, isn’t it?

Jonn Elledge is the editor of CityMetric and tweets as @jonnelledge.