"If I saw a non-uniformed person carrying a fire arm I would call the police."
I hope not. The list of scenarios where it's appropriate to call the Police because a non-uniformed individual is in possession of a firearm is actually quite short.
If you see someone carrying an uncovered firearm, then you're probably in the countryside and they're hunting. Hunters, whilst understanding of public ignorance and paranoia, get really fucked off when armed police come tramping over their permission and scare off the rabbits or foxes they were hunting because a dog walker couldn't figure out why someone in the countryside might be shooting in a field. Basically puts an end to the evening's work.
Similarly, a local clay pigeon site has a public footpath running through the car park. Presumably you wouldn't call the police about this hotbed of gun usage if you passed through on a ramble?
Driving along Queen's Road form Bisley in Surrey you'll pass by the back corner of Century Range at the national shooting centre. On a normal weekend you'll see hundreds of people shooting, none of them uniformed!
Granted, if you see someone ambling down the high street with a rifle over their shoulder then that's probably a cause for concern, but interestingly not illegal provided they have good reason to be carrying - such as transporting it to/from a gunsmith. Thanks to our wonderful mish mash of laws, it'd only be illegal to carry an airgun uncovered. Carrying a rifle or shotgun back to the car uncovered may attract attention but isn't actually illegal!