I have to admit, this has got me baffled.
See, I LIVE in the UK, and I've handed over an unlicensed firearm before now, and didnt get arrested. It went something like this:
My parents had retired and moved to Spain, leaving me in charge of the family home. A couple of years later, I'm tidying out the spare room and what do I find buried under a pile of junk? A World War 2 era rifle (my firearms knowledge sucks, so please dont ask me exactly what type it was). Now, this rifle had been partially disassembled, and the firing mechanism was no where to be seen.
A phone call to my parents gives me the full story: The gun used to belong to my grandfather, and whether or not he had a licence for the damn thing is unknown. My father is sure that the firing mechanism is SOMEWHERE in the house, and even offers a couple of locations I should check. I check, I dont find it. We decide that since there's no licence for this thing (that we know of) we should get rid of it.
I make a phone call to my local police station and explain the whole situation to them, and ask them to please take this thing off my hands as I dont want it. They say they'll send a couple of officers round to collect it.
About an hour later, two chaps in uniform knock on my door. They come in, examine the rifle, ask me a few questions and leave with the gun. At no point was I threatened with arrest or accused of any criminal activity. The closest we got to that was when they explained that the rifle would undergo a strictly routine investigation to make sure it hadnt been used in a crime.
The only difference I can see between what I did and what Paul Clarke did is that I asked the police to come and collect it instead of handing it in...
