Some of the Russell Groups offering Natural Sciences include Durham, York, Nottingham, Exeter etc..., I know some unis will offer intercalated courses where you could study a combination of science subjects/take a joint honours. I think it's really up to you to decide which course suits you and your academic abilities. Are you veering more towards Biological or Physical sciences?
This really depends on what sort of course structure, and which subjects you'd like to do, as different unis offer the NatSci course very differently. For example, Durham offers archaeology, but Bath doesn't. However, Bath and Durham's courses are similar in that they are both structured as a joint honours were you choose a major and minor subject. When I applied, I applied to Bath and Durham for NatSci as I really liked the broadness of the subjects, as this allows you more freedom to choose. However, some people prefer more specific units so would prefer UCLs course structure. From what I remember when I was applying, Bath, Durham, UCL and Cambridge seemed like the best options, but Exeter and Nottingham are also 2 of the top ones for NatSci.
I am in my final year doing NatSci at Bath, so please let me know if you'd like more information about the NatSci course here
Jessica, a final year NatSci student