It's a home office issue because the home office decides whether it is considered public funding. (Which is what I want to know. Obviously, a mortgage lender can refuse me a mortgage for any reason, not just my immigration status but credit, income, etc.)
Here is how it works:
The City Council negotiates to sell homes on large development sites at a discount. So you purchase them at much less than the market price. Therefore, in a way, the council is sort of giving you money. For example, if you buy a house for £100,000 that would sell for £200,000 on the open market, then you can interpret that as the council effectively having given you £100,000.
Which is why I was concerned that the Home Office might consider it public funding.
Persephone, if you're reading, I'll PM you the url from the York City Council website.
Stella Marie, York also has a co-ownership scheme, but this is something different.