The Second World War was responsible for many changes in UK banknotes. The Germans attempted to ruin the British economy by flooding the country with counterfeit banknotes. They nearly succeeded. The fakes were so faithful to the originals that even the serial numbers were correct. Denominations of �5 to �50 were forged. The Bank responded with a series of changes to overcome the problem. All denominations over �5 were withdrawn. We then had to wait 20 years before the �10 was reintroduced, 26 years for the �20 and 36 years for the �50.
The most important change was the introduction of the metal security thread embedded in the note. The idea was developed by the Bank of England Printing Works and was first used on the �1 and 10/- notes issued in 1940 which were also dressed in emergency wartime colours of pink and mauve. A new variety of the White �5 was introduced in 1944. It also had a security thread but the paper was very thick. This proved very unpopular and by 1947 the Bank had reverted to the traditional flimsy paper but still using the security thread.