A new £20 note featuring a portrait of Scottish economist Adam Smith has come into circulation.
The note includes a range of enhanced security measures designed to prevent counterfeiting, such as a wider holographic strip and microlettering.
The new image of Smith will mark the first time a Scotsman has appeared on a Bank of England note.
Current £20 notes, featuring English composer Edward Elgar, will be phased out over the coming two to three years.
An image of Smith already appears on some Scottish £50 notes.
Smith will replace composer Edward Elgar on the £20 note
The Bank of England said introducing the new £20 note would be a major undertaking, as the denomination is by far the most common in circulation.
The Bank said it expected the proportion of £20 notes featuring the philosopher and economist to gradually increase over time.
Bank of England executive director for banking and chief cashier, Andrew Bailey, said the new features - which also include updated security symbols - were the latest step in the "fight to prevent counterfeiting".
"Maintaining public confidence in our banknotes is paramount," Mr Bailey said recently.
Bank of England Governor Mervyn King announced in October last year that he had chosen Smith to replace Elgar on the £20 note.
Smith was born in Kirkcaldy, Fife - part of Chancellor Gordon Brown's constituency.
The economist is most famous for his book the Wealth of Nations, which many regard as almost inventing the concept of competition and market forces.
SECURITY FEATURES - FRONT AND REAR
1. Paper quality -Banknotes are printed on special paper with raised lettering in some areas. Fake notes can sometimes feel limp or waxy
2. Print quality - Numbers, letters and colours are sharp and clear, whereas counterfeit notes may appear slightly blurred
3. Holographic strip - Pound symbol and figure 20 alternate when the note is tilted
4. Microlettering - Words printed below the portrait of the Queen are only visible with a magnifying glass
5. Metallic thread - Silver dashes on the back of the note become a continuous dark line when held up to the light
6. A see-through "register" shows a broken pound sign. The symbol becomes whole when held up to the light.
7. The watermark has been moved to a white panel to make it easier to find
Other - Some unpublicised "covert features" are designed to further deter counterfeiters