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It's one residential property, a normal mortgage would be fine.
But a Grade I Listing is something to be taken very, very seriously. There are only a few hundred Grade I Listed buildings in most counties and 90% of them are churches and castles and shit. You can't paint a wall or replace a broken tile or put up a picture without permission. I'd go nowhere near it unless you get a kick from bureaucracy and have very deep pockets.
In all seriousness, I'm very interested in this: http://www.rightmove.co.uk/property-for-sale/property-63868604.html
Question is, could you get a mortgage on this, or would the bank only lend on the house part?