I think "affordable" is a vague term - but it is not the same as "social housing" is it... The country needs housing for people who are paid low wages - and there are a lot of them. It also needs shared ownership housing so that young people who aspire to get on housing ladder and have a bit more income can start to get a mortgage and stake in a property. When they move on the housing association buys back from them I believe and then finds another shared owner. www.gov.uk/affordable-home-ownership-schemes/shared-ownership-schemes.
In the states they have another model of housing - similar in a way - the condominium in which you buy the internal space but do not own the building in an apartment block. The developer or landlord owns the structure and is responsible for it and a fee per year is paid for maintenance and any shared services (gardens, basement laundry, car parking space - whatever) Perhaps this could be another way forward in this country.
Instead of supporting social housing, shared ownership or new ways of doing things, the present government have been putting money into "help to buy".
On a slightly different tack - I assume that the hundreds of thousands of newer immigrants who keep London and the south east going on low wages (hotels, shops, restaurants, hospitals, office cleaning, construction sites etc) are living in heavily overcrowded accommodation that most UK nationals would not contemplate. Otherwise the economics of the boom-city do not add up do they?