OK, what does your lease say? It should be very specific about landlords and tenants' responsibilities, as to who maintains what, etc. Is the use of the cellar part of the lease?
I'd expect something like steps to be their responsibility, as they are part of the building.
Even though it's a church hall, they must have public liability insurance, and this would be covered by an accident like this. You'd have every right to sue if you wanted to. They MUST have an accident book for users of the hall to fill in - have you done that, you need to in order to comply with H&S legislation.