maybe something like this?
Blitz Standard Reversible Block Body Armour - Martial Art Shop
Under a baggy sweatshirt or something it might not be too obvious.
I totally get what you mean about the UK and it's attitudes towards...well anything really.
Got stopped once walking to the park carrying a cricket bat to - guess what - play cricket. My friend had the ball, stumps and wickets, but apparently I was carrying a dangerous weapon. Go figure
L
perhaps it was the warlike look on your face?