You can no longer spend paper £10 notes in shops and restaurants.
From today the paper tenners are not legal tender in the UK, with banks and retailers refusing to accept them.
The plastic notes have been in circulation since September 2017, as the Bank of England began phasing the paper ones out to be more environmentally friendly.
New tenner: The polymer £10 note with Jane Austen has replaced the paper style ones featuring Charles Darwin
Two weeks ago, estimates from the Bank of England showed there was still £2.2billion worth of the paper tenners featuring Charles Darwin in circulation - or more than a quarter of the total number of notes issued.
However, those who find the old paper £10 notes in the future will be able to deposit them into UK bank accounts at the Post Office.
This is also true of old £1 coins and old £5 notes which have not been legal tender for some time.
The Post Office says any of its 11,500 branches will deposit them – but not exchange them.
Furthermore, if you have found old round pounds, you can donate them to Pudsey's Round Pound Countdown for BBC Children in Need – and Post Office branches accept these too.
Martin Kearsley, banking services director at the Post Office, said: 'We want to remind customers that, even if they don't have a bank branch nearby, they can come to the Post Office to access their bank account and bank their tenner.
'Thanks to an agreement with all UK high street banks, everyone can deposit cash and cheques, including any old notes, into their usual high street bank account at their local Post Office branch.'
Old vs new: The Post Office will allow customers to deposit old pounds and £5 notes into current accounts at its 11,500 branches
If you want to exchange old notes