Rent to buy mortgages?

Anyone have any experience or insight with rent to buy mortgages?
It seems like just an awesome idea for someone like me who rents (and can afford to,but is having trouble scrounging up a 20% deposit for a house because I rent) - and I would like to know more.  But it also seems like there's a catch? 
If anyone has any insight to Scotland in particular, awesome, but I'll take any advise at the moment even if its pertinant to England/Wales.
(Just gathering facts at the moment, as I don't get ILR until the end of this year, so just planning for when I can finally look into getting a mortgage!)

 

I think the catch is that you don't own the house!    It's a shared ownership between you and the housing association.  So you are in their property, paying your rent and a small portion of your rent is going into another 'pot' toward the deposit for the house.  I havent done this myself, but a friend has.  I think that once the 'deposit pot' gets up to more than 25% of the value of the house, you can then offer to buy out the houseing association's majority share.

I've been keeping an eye on this too and from what I can gather so far, on a casual basis, is that these work. I think housing associations put out detailed info and I thought I saw something on council sites. There are schemes for older people and people with disabilities. Google search works. I'm thinking private landlords might do these too. There are rent to buy properties on the internet. Wish I could be more helpful but I just stored the bit that I know for later. Seems I saw good info on directgov site but it might not have explained the private angle. Do look into it, it could be helpful.

Thanks both