Thanks for your patience.
The housing association is unlikely to offer you a mortgage as such. However, they may be prepared to offer you a shared ownership arrangement. This is where you buy a percentage of the property, with the housing association owning the remaining percentage of the property (eg 75/25, 50/50, 25/75).
The shared ownership model is generally used where a buyer cannot afford to purchase the whole value of the property even with assistance from whatever mortgage they arrange.
I would suggest that you see a mortgage broker to determine how much a high street lender (eg. Nationwide/santander/hsbc) would be prepared to lender you. Then, you can work out how much money you have combined with your mortgage and the deposit monies you have available, to see if you can afford to purchase the property
If you do not have enough money with the mortgage and your deposit then you can approach the housing association to see if they are willing to offer you a shared ownership deal for the property
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