You sure it wasn't an lmt defender? They're often used by police, never heard of a 416 though. They look quite similar.
Airsoft Forums UK
CaptainDumbass
HK trademarks..., im pretty sure if was a 416D!
M_P
Fair enough, must've been then 
jcheeseright
416 is in use by SO19.
NickM
Last time I was at Gatwick there was a group of about 8 armed police escorting a police dog team around the departures terminal. Saw them twice I think it was an exercise for the dog as the same people were being "found". But the weapons were insane, not sure why one of them had an MP5 with an Eotech and an Aimpoint Magnifier, not entirely sure what he was expecting to hit with it. If airsofters have a reputation of going over the top with useless sh!t on their rails these police...
NickM
guys looked like they were carrying the "optic thunder" gnu from Evike! There were about 4 different primaries in use and none had the same optics setup?!
CaptainDumbass
3 of them were carrying g36's, a couple with mp5's and a bloke with a 416!
TacMaster
The MP5's considered to be one of the most accurate SMGs available, hence why the officer in Gatwick had a magnifier 
team flex
yeah my mates dad is an armed police officer for Heathrow, uses an mp5
NickM
The magnifier point was two fold, magnifier on a SMG, accurate or not. Second, where in Gatwick would require a shot of a distance that would require a magnifier. Especially inside the terminal.
TacMaster
The departure lounge is pretty big, so are the massive corridors between the gates
Ahem, I mean government.