I think you'll find that the role of the Police is to protect the Queen's peace, protect the public and property - amongst other things), evidence gathering is a facet to that.
You'll also find that incidents of Domestic Violence increase during the festive season - due in part to increased alcohol consumption, families being "thrown together" in stressful situations (Christmas) etc etc
Its well known that incidents of Domestic related murder also increase at this time of year.
It is standard operating procedure that background checks are carried out when the police attend any report of a "domestic" at any address.
Everyone with firearms - be that shotgun or sect 1 has markers on their address.
If theres an allegation of violence at the address, don't be surprised if the weapons and certificates are removed (temporarily) while any allegation is investigated.
If the matter goes as far as the court process - i.e. someone is charged with assault who's a certificate holder they will more than likely be revoked (thats also subject to appeal, but only after the court process)
The simple sad facts are that firearms are rarely used in domestic violence / murder, more likely kitchen knives, hammers, shards of glass,,,any blunt instrument (I've been to many over the years)
BUT the Police will remove any firearms if there is the hint of suspicion or allegation of violence against the certificate holder.
If people don't like it, I suggest you don't have domestics and deal with any argument / disagreement without resorting to raised voices or physical action.
Thats the way it is.
Yes, there are a lot of other arguments around this and one could have a tit for tat repost for a very long time, but as I say, it is what it is, deal with it.