From--http://www.thenewpoundcoin.com
Look like the old one will be Demonetisation.
Autumn 2017
Demonetisation
all your coin handling equipment should be able to accept the new £1 coin.
you are under no obligation to accept the round £1 coin from your customers and you should not distribute the round £1 coin.
the round £1 coin can continue to be deposited into a customer’s account at most high street banks and the Post Office*
*check with your bank for more details, including deposit limits.