It is all about risk assessment and backside covering and I’m bored so here goes.
On your shotgun certificate:- Condition 4 (a)
“The firearms and ammunition [or shotguns] to which the certificate relates must at all times (except in the circumstances set out in paragraph (b) below) be stored securely so as to prevent, so far as is reasonably practicable, access to the firearms or ammunition by an unauthorised person.”
As this condition 4(a) is on your certificate it means firearm security is ultimately the responsibility of you the certificate holder and not the police.
However, when it comes to grants and renewals the law states :-
“28 Special provisions about shot gun certificates.
(1)Subject to subsection (1A) below, a shot gun certificate shall be granted or, as the case may be, renewed by the chief officer of police if he is satisfied that the applicant can be permitted to possess a shot gun without danger to the public safety or to the peace”
Therefore, if the Chief officer of police (represented by the FEO) is not satisfied about your security then they cannot legally grant or renew.
Should this conflict of responsibility become an impasse then your only recourse is for a judge to rule on it, which will more than likely cost you because in certificate disputes costs are not normally awarded unless the police acted unreasonable and unreasonable is set at a very high bar.
If you read BS 7558 which is the British standards for gun cabinets, you will understand their thinking.
It starts off in the introduction by saying they assume the average potential thief is an opportunist and not a determined criminal specifically seeking to obtain firearms, who in their own words would be difficult to counter effectively by inexpensive means. So, they are not interested in that type of thief as they accept you are never going to stop them without a bank vault which is why the “reasonably practicable” bit of the legislation is there.
Therefore, all they want to know is can the cabinet withstand a 5-minute attack from common hand-tools and not noisy power tools or specialist tools or knowledge.
The tools listed in BS 7558 are Club hammer 1.8 kg, Jemmy, Flat cold chisel overall length 200 mm and blade width 25 mm.
If they can get the cabinet off the wall within 5 mins then they can leave with it and take as long as they want to get in and create as much noise as they like, this type of theft has happened hence why they are concerned about it and they specifically mention the type of fixings needed to be used to prevent easy removal in BS 7558.
In the case of the OP I know a FEO has refused this type of installation as he has seen where thieves used a car jack from the home owners garage in the gap beneath to pry it from the wall quickly and take the cabinet with them.
The remedy agreed for that refusal was to coach bolt a large block of hard wood in the gap beneath to prevent a jack being placed underneath.
Obviously, who knows how your FEO will see it but welcome to the world of badly written firearms legislation and conflicting responsibilities at renewal/grant time.