The £50 banknote has lost £38 of its buying power over the past 40 years, according to a finance expert.

Left under the mattress, it would have lost £38.46 of its spending power since 1981, according to Sarah Coles, a personal finance analyst at Hargreaves Lansdown.

She was speaking ahead of the launch of the Bank of England’s new Alan Turing £50 note into general circulation from Wednesday.

Ms Coles said that, having been introduced in 1725, £50 notes were withdrawn in 1945 and reintroduced in 1981.

At that point £50 had the purchasing power of around £217 at today’s prices, she added.

Ms Coles said: “£50 isn’t what it used to be. If you had a modern £50 note when it was first issued in March 1981, and kept it under the mattress ever since, it would have lost more than three-quarters of its buying power.

“However, if you’d put it to work (by investing it) it could have grown to around £2,300.

“By contrast, if you’d put the £50 into a savings account paying an average of 2% over this period, it would have delivered just £110.

“It demonstrates that while holding emergency cash in savings is invaluable, keeping too much in cash over the long term means you risk losing spending power after inflation.”