On my visit to the Portobello Rd. market on Saturday, I found a stall which sells old coat buttons, from various types of official uniforms (mostly of pre-1940s vintage) for £1, and consequently bought 5.
The inscriptions read "BRITISH RAILWAYS", "ROYAL ENGINEERS" and "POLICE FORCE".
The fifth button, a Staffordshire County Police one, is not shown, as is it attached to an old overcoat I have (believed to be of some European military issue) which had lost one of its buttons.
I bought them mostly to replace lost buttons from other items of clothing. I only needed one for that, but I bought several (a) to choose the best-fitting one, and (b) just in case I need the others at some future date.