I honestly don't think you can, I exchanged properties in September last year and it is quite a lengthy procedure. First both of you wanting to swap have to fill in exchange forms, then send to the landlord's. Then a property check has to be done, be aware that no repairs can be carried out for a year. Check with your housing association, but I don't think you can because of assured tenancies Etc..
Thank you for taking the time to answer. I'm still a bit confused [this is for my brother, not me...I'm quite happy where I am thank you very much.....lol]. This is not a scam....just the simple fact that they would be better off with each others properties. Anyway, like I said, thanks for your help.