Minor, and probably specific to busy bars, but it did come up: there's also the practical issue of where you put a £50 note as there's no space for it in a register. So you kinda shove them at the bottom of another stack, but there's the danger that when you're very busy and handing change back you'd grab it without looking. So always had to tell another staff member there was a £50 in the register, and ideally that register got emptied asap.

> During later years of the round pound's use, Royal Mint surveys estimated the proportion of counterfeit £1 coins in circulation. This was estimated at 3.04% in 2013, a rise from 2.74%.[9][10] The figure previously announced in 2012 was 2.86%, following the prolonged rise from 0.92% in 2002–2003 to 0.98% in 2004, 1.26% in 2005, 1.69% in 2006, 2.06% in 2007, 2.58% in 2008, 2.65% in 2009, 3.07% in 2010 and 3.09% in 2011.[40][41] Figures were generally reported in the following year; in 2008 (as reported in 2009), the highest levels of counterfeits were in Northern Ireland (3.6%) and the South East and London (2.97%), with the lowest being in Northwest England.[42][43][44] Coin testing companies estimated in 2009 that the actual figure was about twice the Mint's estimate, suggesting that the Mint was underplaying the figures so as not to undermine confidence in the coin.

[1] https://en.wikipedia.org/wiki/One_pound_(British_coin)

IIRC that is/was only in number though, not total value.