If you still have a stash of English £10 or Scottish £5 and £10 paper notes, watch out - you only have one week left to spend them before they cease to be legal tender.
From Thursday, 1 March the notes will be officially withdrawn, meaning you could be caught out when trying to use them to pay in shops, pubs and restaurants.
Which? explains what you need to know about the change and what to do if you find yourself stuck with old paper money after the deadline.
The paper £10 note featuring the portrait of evolution theorist Charles Darwin will be officially withdrawn by the Bank of England on 1 March 2018, losing its legal tender status.
This means the notes will be removed from circulation and technically businesses no longer have to accept them as payment for goods and services. Shoppers will likewise be able to refuse the notes in their change.
The paper £10 notes will be replaced with the polymer £10 note featuring a portrait of author Jane Austen, which launched on 14 September 2017.
The new Jane Austen polymer £10 note has been designed to be both more durable and safer than the paper tenner, with a host of anti-fraud features.
The withdrawal of the Charles Darwin paper £10 notes coincides with a similar change in Scotland.
The old Scottish paper £5 and £10 notes will stop being legal tender on 1 March. They'll be replaced with a range of new polymer notes from Scottish note-issuing banks - the Bank of Scotland, Clydesdale Bank and Royal Bank of Scotland.
After 1 March 2018, shops, pubs and restaurants don't have to accept the paper Charles Darwin £10 notes or the Scottish paper £5 and £10 notes, so try and spend or exchange them in advance of the deadline to avoid being caught out.
In Scotland, polymer notes have been in circulation since 2015 so the majority of paper notes have been replaced. Polymer notes account for 80% of £10 and 90% of £5 notes currently in circulation according to the Committee of Scottish Bankers.
However, the Bank of England says more than a quarter of the old Charles Darwin £10 notes are still in circulation - that's £2.1bn-worth - so you may well have one in your wallet or at home.
If you discover any paper Charles Darwin £10 notes after the 1 March deadline, there's no need to panic.
The Bank of England guarantees that all banknotes it issues hold their value for 'all time' and promises to exchange old currency for legal tender.
Alternatively, you may be able to take the old notes to your bank or building society or pay them into your account at your local Post Office, though there may be limits on how much you can swap.
In Scotland Clydesdale, RBS and Bank of Scotland will continue to accept all Scottish notes from their own customers.
The issuing banks have also agreed to exchange their own old paper £5 and £10 notes after 1 March from non-customers up to the value of £250.
The Committee of Scottish Bankers has confirmed that other banks, building societies and the Post Office may continue to accept and exchange Scottish paper notes after 1 March.
The Bank of England has been rolling out polymer notes to replace the less-secure and easily damaged paper versions since 2016.
The paper £5 note, featuring the prison reformer Elizabeth Fry, lost legal tender status in May 2017. It was replaced with a polymer £5 note that bears the image of former prime minister Winston Churchill, which was launched in September 2016.
The paper £20 note featuring economist Adam Smith will be the next one to go, replaced by a polymer note with the image of painter JMW Turner in 2020.
The Bank of England has not yet confirmed whether the £50 note will be replaced by a polymer note.
You might want to hold onto old paper notes in the hope that their value may rise after they are removed from circulation.
However, it's rare to find a banknote that is considered a collector's item.
Generally speaking, notes that are among the first to have been printed - with a serial number of 'AA000200' or lower - can be in high demand. Unusual serial numbers, or those with formations that might be considered lucky or significant such as '88888', can also be of interest to collectors.
But notes will usually need to be in mint condition, so if you have a crumpled or torn paper note it's unlikely to go for much.