Small Data: Check for fifties under the mattress
The £50 note featuring the first governor of the Bank of England, Sir John Houblon, will be withdrawn on Wednesday after 20 years in circulation, writes Anthony Reuben.
The Bank of England withdraws notes every now and then so it can replace them with new notes that are harder to forge. It reckons that with two weeks to go there were still 53 million of them in circulation, with a value of £2.65bn.
That seems like quite a lot - I can't remember the last time I saw a £50 note.
"We'd expect a lot to be out there," says Victoria Cleland, head of the notes division at the Bank of England (remember her name - you'll start seeing it on banknotes soon).
"There was an increase in demand for fifties during the financial crisis," she adds, as people worried about the safety of banks.
She also says that some people use larger denomination notes to save up for something, and those people might well keep their Houblon £50 notes until they are ready to make a purchase and only then come to the Bank of England to convert them to current notes.
We know that high-denomination banknotes are popular with criminals because they make it easier to transport lots of cash, although the most valuable euro note - the 500 euro - is worth eight times as much as a £50 note.
Anyway, if you are more cash-oriented than I am, and have a stack of Houblon fifties under your mattress, you only have a couple of days to get down to the shops for a spending spree.
Post Offices and several banks will continue to accept them until the end of October.
After that, if you want to exchange your bills for one of the new Boulton and Watt £50 notes, you'll have to get yourself down to the Bank of England in London (go to Bank station - it's easy to remember) or send them in the post.
If you fill out a form, they will exchange any Bank of England note ever issued for its face value.
The Bank says it exchanges about 1,000 notes a month.
Have you got an Isaac Newton £1 note or a Duke of Wellington fiver lying around? The Bank estimates there are still about 80 million Edward Elgar £20 notes - an extraordinary £1.6bn-worth - out there somewhere, four years after they were withdrawn.
The Bank will even exchange pre-decimal notes, so if you have a 10 shilling note at the back of a drawer, they'll give you 50p for it.