My only concern would be changes in building code since the place was built.
Legally grandfathered in does not mean an appraiser won't ding you for the trouble it presents for potential renovations.
Over here, if permits are pulled to work in an area of the home, everything going on in that area has to be brought up to modern code. That's why you see home reno shows fussing over knob & tube and stair treads, it's not a choice once they're working on it.
Here, attached barns have to have a certain number of feet of open-air space (a roofed alley) between the dwelling space and barn (mitigating the risks from fire).
The barn also has to be a certain number of feet from food prep - the kitchen.
When I was a teen we rented a house-barn for our horses during show season. We found out it was not up to code because although it had the open alley, it opened right into the kitchen, failing the distance minimum. Updating that house to modern code would have required moving the kitchen, which is why the kitchen hadn't been renovated since the law changed, as pulling a permit would have forced the move.
Of course, this is a different country. I would just look at what's on the books about it, so you are prepared.
Even if it's a ding, it may make no difference whether animals are presently in it or not. So there may be nothing you can do to avoid it.
I'd also be really aware of the appraiser being a potential reporter of any active code violations you are not protected from by grandfathering... ie number of chickens, etc. It's easier to hide some birds at a friends than to deal with that rot.
*ETA: Oops! I missed the "New" in front of England
