The guinea was the major coin of the eighteenth century, but during the long war with France the banks began to issue notes in place of coins.
The issuing of bank notes helped Britain to pay for its long war, but it caused inflation and national insecurity and a spate of forgeries took hold. You can view many of the old records of cases brought at the time on The Old Bailey website.
Following the defeat of Napoleon at Waterloo in 1815 the decision was taken to undertake a ‘great reform of the coinage’. Gold was adopted as the ‘sole Standard Measure of Value’ and bank notes were taken out of use.