Hazel Blears MP said last night at a Labour Party Conference fringe event that affordable housing in London under Mayor Boris Johnson could be under threat and lead to the creation of ghetto cities.

The Secretary of State for the department of communities and local government said that Johnson was moving away from former Mayor Ken Livingstone's affordable housing percentage towards a damaging alternative.

She said that it was important that developers and local authorities were not allowed to substitute affordable housing for sums of money or provision of social housing 'off-site' and not within a development to avoid 'ghetto cities'.

'I had Boris Johnson in my office two weeks ago and I would be keeping a very close eye on whether every bit of affordable housing is reduced to a sum of money as it is very important to have integrated communities and we should not be dumping people into a ghetto,' she said.

'Boris Johnson seems to be thinking about affordable housing in terms of numbers rather than a percentage and sharing out the numbers among the London boroughs. A lot of them [boroughs] are already looking at where they can put it and I am not saying that anyone is doing this but I don't want to go back to a situation where gerrymandering takes place,' she said.

Blears was speaking at a fringe event hosted by the Urban Hub and Westfield on issues facing cities.

A spokesperson for the Mayor of London said: 'The problem with the previous Mayor's inflexible borough wide target, that 50% of all new home should be affordable, is that it did not work. For the past few years barely 35% of all new homes delivered were affordable. Working with the boroughs rather than dictating to them will ensure we build 50,000 affordable homes over the next three years and there is no question that we will allow developers to abdicate their responsibility to build mixed communities. These are essential to the successful development of the capital.'