what they said ^ definitely pick your favourite subjects to make A levels enjoyable and grades better. Having said that maths is super useful in this subject area.
Do you know which bits of Enviro Science interest you? - its fine if you don't (look at some Uni programmes / modules if it helps. You can always choose a more flexible Uni programme with lots of options), its quite a broad subject area with lots of potential directions afterwards. FWIW my eldest daughter started here (sort of), got interested in the politics side more and went to do that. My other daughter started here and biased towards conservation biology
Have to ask, why Russell Group? You know its just a club of Unis that bid for research funding? It can be nice to have research informed teaching at UG but some RGs don't have the best teaching quality.
There are some other excellent Unis in this space, Lancaster for one. During our tours of Uni Open Days I have to say Sheffield Hallam made the biggest impact, the staff were so enthusiastic - do pick the Uni for the course, and think about Uni industry connections, placement years etc too because it will help a lot with employability