[simonmark6]

I'm happy to try and answer this, but I hope it doesn't collapse into an argument about UK gun laws. I know that wasn't the intent of the post so:

In 2007, England and Wales had 3,400,000 registered firearms. All of these would be shotguns and rifles, mostly in private ownership. Numbers for Scotland were 240,000 and Northern Ireland, 380,000. Average number of guns per 100 people would be about 6.

This was 2007, in a TW2K environment there would be more guns although semi-automatic guns with magazines would already be gone after the Michael Ryan massacre. The Lockerbie massacre happened in 1996 and led to legislation to ban handguns. The ban and collection of weapons didn't really start until 1997 however so it might not have been as successful in a TW2K world and, indeed, it may not have gone through in a world with escalating threats of violence.

In general, you can have five shotguns on a shotgun licence as long as they have a capacity of three rounds. Larger capacities go on your rifle licence. All rifles will generally be bolt action or low capacity semi-automatic and pump-action in no greater than .22 calibre although pistol calibre lever action guns are also present. Bolt action and lever action can be of most calibres and magazine capacity is not limited. Semi-auto rifles of larger calibres can be used but have to be converted to single shot so that the action must be manually cycled every shot (making them awkward bolt actions)

Gun clubs usually have small calibre target rifles of .177 and .22 calibre. Usually.

Another place you could get limited firearms would be a Cadet hut: many big guns were pulled in after the IRA started raiding them for weapons so most would be air rifles or .22 with the odd Lee Enfield or single shot SA 80.

Looking at a TW2K scenario, guns could be relatively commonplace: the population has reduced from 60 million to about ten so they could be very common, as much as 1 in 10 or less to really rare, it depends on how many were lost or damaged in the chaos.

I'd guess that lots of guns were cherished over human lives in the chaos and that there would be a lot more guns per 100 survivors than there are now. Most will be double barrelled shotguns and .22 rifles but there will be enough other guns to make things dangerous.

Ammunition is another issue: I doubt there'd be a lot of bullets left unless there was a local reloading industry. If I remember rightly, you can't keep more than a hundred rounds of any calibre.

Hope this helps.