In the US both of those would have been handled with an Investigatory detention - same as being pulled over for a traffic stop. Not even remotely an arrest.
> They did however arrest me so that they could do a formal search and had right to as they had reasonable suspicion I was carrying it as a weapon.
What "reasonable suspicion"? They could see the "weapon" that had been reported and at that point it should have been "have a nice day" and then them trundling themselves over to whoever called it in and charged them with making a false report.
I swear, UK police seem generally nicer than US cops but infinitely dumber and the shit you brittons put up with in terms of having your rights violated is astounding.