Interesting thread, myself and my fiancée are currently waiting for our completion date on our new house and have suffered many of the same woes as the OP. All valuations etc done
finally!
We are buying 60% shared ownership house, as the OP pointed out having the rent increased in an issue but after using their calculator it can only rise around £8.75per month, fixed for 1year. So a maximum of £105 rise per year possible.
We didn't have a very big deposit (approx 7%) but I still managed to find a rate of 3.99% fixed for 3 years with a LTV of 93%. However, the "independent, whole market mortgage adviser" our housing association recommended we use said the best deal they could offer was 5.74%, so my advise is shop round. Anyone thinking of having a shared ownership mortgage check out:
http://www.sharetobuy.com/ some lenders won't deal with mortgage brokers (Co OP and HSBC to name two)
Issues we have had:
Lender - Co Op, who have taken over 2months to complete our mortgage agreement from the initial principle agreement, it seems at every stage it would need to be "assessed" and that would take a week, just for them to come back and ask for another document. We at no point took more than 24hours to send off anything they asked. Knowing what I know now I'd have gone into a Co Op bank to arrange it, it was by far the best deal about so we had to stick with it.
Solicitor, who managed somehow to do searches and draw up a contract together with the map showing the boundary of the property of the house next door. Which would be an easy mistake except the map had all the house and plot numbers written on it. They have also sent us paperwork for another client who is nothing to do with us.
My general impression is the whole process of buying a house needs to be looked at starting with the legal side, it's scary I can phone up my solicitor and he only asks for my surname and is happy to give out any information I ask for over the phone while the Co Op make me answer 4-5 security questions every time I ring up.
I can't say I'm looking forward to having to deal with chains or estate agents, it's been long winded enough and we are buying a new house with no chain.