For one thing, it probably wouldn't be the Guards. Revenue have been around a lot longer and have search and seizure powers the cops can only dream of.
However, I think that argument would work. The letter of the law is "No person may ... Have or use a still for distilling, rectifying, or compounding spirits"
The operative word there is "for": as long as you can prove it's for some other purpose, you should be in the clear.
But don't quote me. If Revenue feel like hanging you out to dry for it, they probably will.