That will have been financed separately.
Big projects usually involve a consortium. If you look at the big boards outside a new construction site, it will often tell you who's involved, which might include
- Always the developer (Brent), whose stake will be relatively small (5% to 15%?)
- Always a financial institution or group of financial institutions (always the biggest slice (60% to 85%)
- Sometimes the construction company (5%?) as an investor - most large construction companies also dabble in development.
- Sometimes the intended operating company where that's separate from the occupier (e.g. in PFI type deals) - most operating companies are associated with large construction companies
- Sometimes the intended occupier
- Sometimes other parties who have an interest in the outcome (e.g. local or central Government, where they have an interest in the finished article),
Without that package in place, the project won't start.
Almost always the project will be sold on once completed and in successful operation, usually to a commercial landlord or a pension fund and the original investors are paid off.
So, to answer you question, I'm sure Brent retains an interest in the ice rink, offices etc as developer, unless he's sold it on already to another developer off the drawing board, but the bulk of it will come from financial institutions, which is absolutely normal.
All that's been said suggests the club owns the land on which the grandstand is being built, that Hallett is involved only in the football club part and that (unusually) Hallett has financed the whole thing 100% by a loan to the club, which is on very beneficial terms for the club.