Our story began:

Birmingham has been offered control over rail and bus services, job centres and further education - if the public decides it wants an elected mayor.

The Government is offering the city the chance to grab power and money from Whitehall, if voters choose to introduce a directly-elected mayor in a referendum next year.

But although Ministers are "not ruling out" devolving power even if voters reject proposals for a mayor, the chances of the city grabbing real authority for itself will be reduced.

In the story we quoted Greg Clark, the Cities Minister, who said in a briefing with regional journalists in the House of Commons yesterday:

We are determined to decentralise powers but clearly one of the reasons for having discussions with each of the cities is that their capacity to take on some of these powers and services will vary from place to place.

It is clearly the case that where you have strong leadership and a clear mandate for that leadership, that is a great advantage.

We are not ruling out other arrangements being considered.

But it is clear that the government has always thought that having a directly elected mayor provides that kind of visible leadership that is necessary to be able to conclude these deals.

The headline in the print edition of the paper was: "'Elect a mayor and win more powers' Pledge". The headline in the web edition was "Elected mayor referendum gives Birmingham chance to take control, claims Clegg", which wrongly attributes views to Mr Clegg which were actually expressed by Mr Clark - although as Government ministers they are supposed to be bound by collective responsibility. We are correcting this.

The office of the Deputy Prime Minister has contacted us to make it clear that Mr Clegg has not said that cities need to elect a mayor in order to access greater powers. They e-mailed over a comment made by Mr Clegg during an interview with BBC Look North this morning, in which he said:

There is absolutely no link whatsoever between our offer of new powers to these cities and whether they vote for a mayor or not.

So you could have these new powers whether you've got a mayor or not. All we ask in return as a Government is that, whether it's a mayor or whether it's a council leader, there is strong, clear leadership in our cities in order to be able to see these City Deals through.

Clearly I either misunderstood what Mr Clark is saying or Mr Clegg and Mr Clark are saying different things. I think it is the latter.

And in fact, a Government document published today to coincide with Mr Clegg's speech, called "Unlocking Growth in Cities", seems to confirm that cities with mayors will find it easier to win new powers.

Page ten of the document states:

leadership and accountability: where cities want to take on significant new powers and funding streams, they will need to demonstrate strong, accountable leadership, an ambitious agenda for the economic future of their area, effective decision-making structures, and private sector involvement and leadership (cities with a directly elected mayor will meet this requirement);

And on page 21, the document states:

appropriate governance and accountability: before devolving powers, the Government will need assurances that there is visible and accountable political leadership. [My emphasis]

Important ingredients that we are looking for are:

a clear mandate to drive an ambitious economic programme over the medium term;

the ability to work effectively across boundaries, build informal coordination arrangements and take strategic decisions across the wider economic area;

visible leaders that businesses can deal with, that communities can come to and that central government can negotiate with; and

clarity over who is responsible and accountable for taking actions to support economic growth. Cities that have a directly elected mayor will be well placed to meet these tests. Other governance arrangements will need to demonstrate how they will do this. [My emphasis]