Having worked in casino's in the UK, I can only think that it would be for placing a section bet on roulette. The places I worked did not use plaques on roulette, but there are 3 popular sections to bet, and each uses a different amount of chips.
A £45 amount would be for a standard nine piece bet. Check this out for more info on strange British betting on roulette.
http://www.virgin.com/content/games/howtoplay/roulette.asp#standardbettypes