My experience may help as i have just sold a shared ownership in Staines. Things to remember are that although I spent £20K on improving the property the HA still got 50% of the price I sold for. Improvements are only taken account of if you staircase apparently. This was an older property and when I went to sell I found the lease was less than 70 years and I had to spend £10K renewing the lease with the HA who then renewed with the superior landlord for £10K, ie I paid for it all! Without the new lease it was unmortgageable. Generally shared ownerships are new properties, but always check the lease. Finally, the HA had it valued by a chartered surveyor and this became the selling price. The purchaser then had it surveyed for his mortgage and they valued it £20K less than the HA, which affected the mortgage he could get. There is no doubt the HA overvalue the properties so watch out for this and get your own valuation. Ultimately, I sold it for £20K less than the HA valuation, or I would never have sold it.
As the price went down I suppose the only way I made anything was that the HA took half the loss!
Also, the purchaser was within the stamp duty threshold and did not pay any, but if he staircases above the threshold he will become liable for it all.
Remember as well that when you come to sell you have to sell to a HA applicant and rely on them marketing it properly.After a certain amount of weeks if they do not find a buyer you are free to sell to who you want through your own agent. Either way, you pay all the selling costs regardless of the percentage you own.
Generally, you do not make money on shared ownership and unless it is the only way you can get into the market I would avoid it. If it is the only way, then make sure you get an independent valuation and negotiate the price. It proved more trouble than it was worth in my experience!
Hope this helps.
Elaine