The old round-shaped £1 coin became invalid in October 2017. Some of them are in high demand among collectors. Some of them are being sold for over 30 times its face value.
The Edinburgh City (2011, Scotland) coin is the rarest £1 coin in circulation which has a market value of £34. Only 600,000 to 800,000 such coins are in circulation. Second in line is the Cardiff City (2011, Wales) £1 coin which has a market value of £5 to £30. The London City (2010, England) £1 coins are the third rarest which are also being sold for anything between £5 and £30. Thistle & Bluebell (2014, Scotland) coins in excellent condition are selling for up to £10 on eBay. Crowned Shield (1988, UK) coins have a market value of £6 on eBay. The Rose & Oak (2013, UK) coins are being sold for up to £15. The Flax & Shamrock (2014, Northern Ireland) coins have a market value of up to £34 on eBay.
Other rare coins in demand include Daffodil & Leek (2013, Wales) coins, Belfast City (2013, Northern Ireland coins, Lion Rampant (1994, Scotland) coins, Millennium Bridge (2007, England) coins, and Flax (1986, 1991, Northern Ireland) coins.
So check your change now, you could get lucky!