hmmm well my advice would have been not to get pregnant again when you knew you were in a small flat. Contraception is free, flats are not.
if you want a bigger place may i suggest that you stop relying on the council to house you and your family and maybe do something about private renting ? then you have control of where you live, and dont have to go by their rules. You could have a bedroom for every child then if you wanted. it probably sounds like a harsh reply, but there are people who cant even get a council place or who have a lot more problems than you health wise, or the health of their kids, so i can't see why you would necassarily be a priority really. Having children is a lifestyle choice, so if you cant afford to house them, or are not happy with the social housing you are offered don't have them, simple!