Around £145 million old-style £1 coins are missing in the UK.
The round £1 coin was replaced by a new 12-sided version, and the old ones became non-legal tender in October 2017, which means you cannot spend them in any shops. Since then 24 million have been returned to the Royal Mint. They can be deposited in banks, but a lot of people have obviously not bothered.
I have checked my piggy bank, but none of them are there.