Are you watching Farage!
There are a few countries already in the EU who have no plans to adopt the Euro. I’m sure we could do the same.
If I understand correctly, they are countries that joined before adopting the euro was a prerequisite, which it now is.
It may have changed recently, but my understanding of it is that you are expected to aim to join the Euro but there is no set timescale.
The ECB summary seems to indicate that they would rather a country is in a stable, fit condition before adopting the Euro. (We probably have Greece circa 2008 to thank for that.)