@ineedaholidaynow
Did he belong to a gun club?
If his shotgun was a Section 1 shotgun, more than likely he would have needed to be, or needed to be involved in something to justify it, like partaking in practical shooting competitions.
If the shotgun he used was a Section 2 shotgun, he wouldn't have needed to be.
Section 2 shotguns for anyone wondering are standard double barrelled shotguns, either side by side or under/over, and semi automatic and pump action shotguns with a capacity of no more than 3 shells in total. Section 2 shotguns are granted on a SGC (Shotgun Certificate), pretty much any person in the country is allowed to get an SGC and shotguns and you do not need a specified reason for wanting them, at that point it's up to the police to prove a good reason why you shouldn't have them. You can also buy as many section 2 shotguns as you want once you have a SGC there is no restriction on numbers, only limiting factor is having the correct amount of space to store them safely and securely.
In contrast, a FAC (Firearms Certificate) covers pretty much everything else you can legally own, Section 1. This includes semi-automatic and pump action shotguns with a capacity greater than 3 shells. The granting of an FAC is different to the SGC in that, you need to demonstrate good reasons to the police why you are asking for each firearm you've listed on you application; e.g. target, pest control, practical shooting, etc. You are also restricted on how much ammunition you can hold at any stated calibre, and if you're found to have more than your allowance you risk losing your firearms. Standard bird/buck shotgun ammunition is not restricted and anyone with an SGC/FAC can buy as many shells as they want. If you don't have membership to a club, or registered training and memberships under your name, you won't (or rightfully shouldn't) get granted an FAC.
It's uncertain at the moment, whether he used a Section 2 shotgun, or a Section 1 shotgun. But Section 2 shotguns are obviously easier to get than Section 1 variants.