Hello, I am Keith, one of the experts on Just Answer, and happy to help you with your question.
My immediate reaction is 'So what?' You are not buying a business, just landed property. Presumably the Church was registered for VAT as a business at some time. In my opinion the solution to this problem is simple. Before your solicitor completes the conveyance make sure the vendor de-registers the old business.
The fact that the original business was registered is no concern of yours and any buildings you erect would be outside the scope of the business currently registered. That is, of course, assuming that your own business is not registered for VAT. If it is then your buildings, if erected by your business as opposed to you personally, would come within your business's VAT envelope; but not the other's VAT regime.
If it has not been removed you merely use VAT Form 7 to deregister, but it really is the existing owners responsibility. This form is available on the web here:
You really do not have to worry overmuch about this and in any event the solution is simple. I do hope that my reply has been of use to you.