The environmental sector is a big and varied thing. At the one end of the spectrum you have the charities (Wildlife Trusts etc) running nature reserves, then there are the consultancies helping developers to work within the legislation, and within that there are consultancies that purely deal with plants, animals and habitats (ie, ecology), some that purely deal with chemicals / drainage (ie, environmental science etc.) and others that are part of massive engineering consultancies.
Beyond that, there's the technological end of things - sustainable technology, renewables, insulation etc. etc.
Very different skill-sets and prospects in each sub-sector. It's not like going to be an accountant, where everyone trains to 3 or 4 main and similar standards.
In my view, there is no point in anyone going into the ecological end of things with a view to improving employment prospects beyond the level of "having a degree". The sector is very competitive, and it's one a lot of people are happy to volunteer in. End result is that hours and pay get pushed, and a lot of of charity jobs go to people who volunteer a lot.
On the other hand, the environmental science / engineering stuff is seen as a little more difficult and I suspect is better paid as there's far more potential for specialisation, and obviously there's no prospects for volunteers etc.
The renewable / sustainable tech side of things is likely to become more important, but I don't know much about it. I suspect it would be fairly useful across a good range of industries, and I'd be particularly keen to take any optional business modules, as it could skill you up to be a good fit for a management role in any business that's trying to improve its environmental performance. Generally good environmental performance can go hand in hand with improved business performance (ie, reduced waste).
Another point is to make sure it's as good a uni as you can get into, and that you get decent A-level grades. A hell of a lot of employers still want to know A-level grades, and a lot more only recruit from 60 or so "top" universities. Don't just go somewhere because the other place is stuck up or a bit further away, or because they've given you an unconditional offer! There are generally good opportunities during clearing if you miss your grades - my girlfriend got into a uni that wouldn't have had her according to their published minimum grades.
