Are there not lists of people waiting for affordable housing ? You say that you're having trouble to sell it. Surely, if you work with the council you can pass it onto the next person on the affordable housing list, for the same/similar price to what you paid for it. You're not supposed to make money on this type of house anyway, as far as I know. These houses exist for a social reason, not to provide people with a second/rental property.
Surely, if you received a house under this scheme, the right thing to do is to sell it on to another person under the scheme?
Only new properties are available under the affordable housing schemes.