Just seen this thread and its made me think back, my parents bought me some premium bonds about 20 years ago. Not much, about £1k, but worth looking into! Looks like you can ask them to search for accounts you've lost details for so going to start that process. Not expecting much, but even the original amount would be nice.
Personally I think I'd take the money out and put it in my stocks and shares ISA, I'm up roughly 16.5% in 2024 already so much better return than others here are getting on Premium Bonds.