Sorry for the late reply, but here’s my pennies worth from a AF44 member.
Back in 2014, at local events, in the area I live, we had cosplayers attending events with Airsoft RIF’s.
We’d once had the police called on a guy at an event dressed up as Hawkeye from The Avengers for his plywood bow and arrow but he was near a major roadway and obviously spooked a member of the public.
The Armed Response Unit turned up, saw the likes of COD/MW characters, a guy from Hitman, a friend as a T-800 with a minigun and I was part of a Resident Evil group in my Hunk-cum-Centurion mash-up.
The police recognised what was going on after that and have since made an unofficial attendance at the events from now on, as closet-cosplayers no doubt.
Even at the London MCM event, it wasn’t an issue. They were a bit more rigorous with checking however.
Then on May 22, 2017 in Manchester, UK at the Ariana Grande concert at Manchester Arena, a suicide bomber blew themselves up killing 22 people and injuring 800 more.
It has nothing to do with cosplay, it had nothing to do with cosplay props, but the UK went pretty much hiked up security nationwide and cosplay events, with people having military-themed costumes, anything intimidating or threatening in terms of props was frowned upon.
I’d just made a box of pretend explosives, such as C4, landmines and an IED for my Firefly cosplay, but it has never been to an event because you can’t judge the reaction of the public.
At big, major events, you hardly see RIF’s at all and people stick to Nerf weapons but security see a weapon and scrutinise it.
At local events, the event organiser Lee, has known me for 10 years and knows with my Firefly, Umbrella Corp, Sith or Hostel cosplay, it incorporates weapons but I always identify myself to him and allow him to inspect what I have, although he never does. Given his level of trust for me, he knows me well enough to be both sensible and responsible both in and outside the event.
But away from my local area, it’s a different matter. If I go with a group, sometimes they have a group/guest dispensation. If I’m alone, it’s weapons that are visibly toy-shop cap-guns.
Having looked into going to Ireland for Dublin Comic-con, the ferry service DFDS said I would need a firearms license for my airsoft RIF’s, so if I can get away with avoiding pistol/rifle props, I choose another costume.