My dad got involved in a fight in Plymouth in the middle 50's (iirc) the other chap pulled out a straight razor and tried to slash my dad's face. There's a very thin, very small scar on the end of dad's nose where he got clipped. Fortunately, there were 2 Royal Marines watching from over the street, Dad was in the Royal Navy at the time, they gave "razor boy" a proper shoeing.On the other hand my father remembers the problems with knives in the 60's and 70's...
His comment on Peaky Blinders "yeah they used to do that", he grew up in Newcastle in the 50's in an area that was not the best, and IIRC the razors in hats thing was copied by some of the mods/rockers gangs in the 60's as well.