These are the reasons for revocation of a firearms licence:
. The grounds for revocation or partial revocation of a firearm certificate are satisfied if the chief constable has reason to believe either:
(a) that the certificate holder "is of intemperate habits or unsound mind or otherwise unfitted to be entrusted with a firearm"; or
(b) that the certificate holder can no longer be permitted to hold the firearms or ammunition to which the certificate relates without danger to public safety or the peace; or
(c) that the certificate holder is prohibited from possessing a firearm;
(d) that the certificate holder no longer has good reason to possess the firearm or ammunition.
The fact that a person is stressed and is on anti-depressants could easily fit the first category. The decision is that of the Chief Constable in the licence holder's area.
If you are a memebr of BASC, try their legal department, they are very helpful.