Affordable home building in London has increased by more than 15 per cent in the last year, breaking the previous record for the number of new starts.

There were 14,544 affordable homes started in the capital last year, up from 12,555 in the previous year.

This beat the Mayor’s minimum target of 14,000 new builds – but was still towards the bottom of the target range, which aimed for up to 19,000 affordable homes to break ground this year.

And the figure is still well below demand, with the Mayor’s Office estimating that 43,000 new affordable homes are needed each year in London.

The Government defines affordable rent as 80 per cent of normal market value – but the Mayor’s Office argues that for London, genuinely affordable rent should be between 40 per cent and 60 per cent of private rates, roughly corresponding to traditional social rents.

Only 27 per cent of new starts last year – a total of 3,991 homes – were at social rent levels.

London Assembly Conservative group leader Gareth Bacon said that lack of affordable housing remained a major problem for London.

He said: “The Mayor is not building the level of affordable housing that he claims that he should be. Even though he’s making big bold statements about how much he’s doing he’s not actually doing very much.”

But the Mayor said the accusations were unfair, and real progress was being made in providing homes for Londoners.

Mr Khan said: “I’m really proud of the fact that last year we broke the record for the most number of homes started that are genuinely affordable since the powers were devolved to the mayor.”

He added: “You’d expect a reasonable person to be saying, ‘Well done, we should be more ambitious next year’. But the thing with the Tories is that they’re never reasonable.”