A close ally of Andy Burnham has criticised London's poor housebuilding rates and questioned whether Sadiq Khan is a 'really focused and functioning mayor'.

Jim O'Neill, a former Treasury minister who has advised the Prime Minister, took a swipe at Lord Khan as he bemoaned how 'momentum has gone from London'.

He added that London's economy had 'slowed significantly' over the past 20 years and is 'not firing on the cylinders we once all expected it to be doing all the time'.

'Obviously the mayor has not managed to build a lot of houses, despite often stating that ambition,' Lord O'Neill, a crossbench peer, told LBC.

He also despaired at Lord Khan's failure to reopen Hammersmith Bridge, which has been closed to all motor traffic since April 2019 due to safety concerns.

The continued closure of the 139-year-old bridge in South West London has caused misery for drivers and dire congestion at other crossing points over the River Thames.

'Here's something that for nearly, what is it, eight years, absolutely nothing happens about,' Lord O'Neill said.

'And it sort of epitomises the seeming never-ending inability of London to get anything done.

'A really focused and functioning mayor, you would think, would be capable of doing things about something like Hammersmith Bridge.'

Lord O'Neill made the comments as he gave his backing to the bid by Mr Burnham, the former Greater Manchester mayor, to devolve further powers to England's regions.

'Ironically since Greater Manchester's done so much better and the sort of pioneer of these tentative movements, London has actually slowed down dramatically,' Lord O'Neill said of devolution efforts under previous governments.

'And the reality is, if you want to take the approach of trying to get better overall growth by getting more regions having growth, you've got to do something about London.

'So, and it's quite ironic, of course, for a Government that's arrived because of what's going on outside of London, but I think there's a lot of big forces that have happened since the financial crisis that's probably behind parts of London's weakness.

'The peaking of the property market in 2014-15, and actually I think Brexit had much bigger negative fallout than anybody anticipated in advance for London.

'And so, it could be a lot of those forces, but it might be something that's wrong with the mayoral model as well.

'It often seems to me, from the little I know about the London model, that they don't have as many powers or they're not as cohesive as the likes of the Greater Manchester.

'So, I don't think it should be seen, as I often read it, about the whole of this sort of focus is sort of further problem for London.

'I think London needs specific attention myself, because it's so important to the overall economy.'

Asked about Lord Khan's record in charge of the capital since 2016, Lord O'Neill added: 'I suspect there's, you know, it's not straightforward.

'As I say, I think there could be some big forces going on that have absolutely nothing to do with them there.

'One of the side consequences of something the Osborne and Cameron government did that I don't think they realise is when they increased or raised taxes for overseas ownership of rented property in London, it sort of broke the economics of the model of buy-to-let, and whether that was responsible for it on its own is hard to say.

'But ever since then, back in 2015, the London housing market has peaked, which of course for affordability is probably not a bad thing in the long term, but it's meant a lot of that momentum has gone from London.

'And then of course the whole thing with Brexit meant a significant absence of foreign buyers coming from Europe for the property market.

'But more importantly, it seems to have had quite a marginal negative influence on many other things to do with the interplay between London's role as the sort of capital of the Western world in terms of time zone for everybody, etc, etc.

'And so, there's all of those things which might have absolutely nothing to do with the mayor, unless you give the mayor increased powers.

'What when I look at it specifically about the mayoral model, obviously the mayor has not managed to build a lot of houses, despite often stating that ambition.'