My view is that one should always support the Police in the interest of a peaceful society, and to uphold the law. However where a Police force is attempting to extend their authority further than the law allows for, then this needs to be politely, but firmly, challenged. It is for the courts and Parliament to interpret and make the law, the Police are there to uphold it.
Whilst it is reasonable to expect Police to exercise discretion where the law allows for it, it is certainly not acceptable for the Police to extend their authority where the law does not make such provision, particularly when there is no clear threat or issue that requires this action. It is unacceptable for the Police to threaten actions which would not stand up in court on the basis that the subject is unable to defend themselves. That is a very short path to tyranny..
There have been a number of technical developments such as Bump Stocks and MMARS actions which have appeared to try and circumvent the rules on automatic and semi automatic firearms. I have some sympathy with the authorities over their attempts to control such developments within the law, particularly where the need for such devices and the motivation of the users is questionable. The position regarding muskets however is fundamentally different. Smooth bore, muzzle loading long arms loaded with a single ball have been in continuous use in these islands from at least the 15th Century. They have been used for sporting, defensive and military use over the centuries and have featured in legislation many times over this period. The Police cannot claim that they are something new, creating a novel threat that could not have been anticipated by the drafters of the law.
UK firearms law is a mess. Instead of maintaining a central element of coherent law, the situation has been allowed to develop piecemeal, with bits of legislation scattered across numerous acts as a result of political point scoring and knee jerking. Most of the recent elements have been badly drafted by largely ignorant administrators overly influenced by unrepresentative pressure groups. That said, the UK firearms law generally works, and provided an individual has a reasonable purpose for possessing firearms, there is usually not a problem. The UK media however has a view that "everything is banned" and that any incident involving a firearm is a cue for more "investigative journalism" and chest beating complaints to "tighten up the law". The Police are clearly influenced by this, and have a habit of playing along.
The Police are not the Law, and must gently be reminded of this when they forget...!
If the Police have a concern with Mr Smoothie's use of firearms for rabbit and squirrel control, then they need to make this case. I have no knowledge or understanding of Mr Smoothie's character or intention, however if he presents a threat to public safety by his activities, then there are other ways to challenge him. Frankly, if he poses such an unacceptable threat to the extent that the Police are making up new law, then perhaps he is not a fit person to possess even a shotgun licence? Again, I would suggest that the British Association for Shooting and Conservation might have a view...?