To specialise or not to specialise?

It would be easier if you said what you were actually studying, and what you were considering specialising in. I do Physics, and what I would say is the parts that you think you enjoy about your subject won't necessarily still be like that after a year or two. University teaching methods are much more rigorous and you will likely discover that what you think you know about your chosen specialism is actually either wrong or only applicable to a specific case. The advice I would give would be to stick with a general subject, and just specialise in the modules that you take. When it comes to a masters, that's the time to specialise, not before. And as for getting a job, if you want to work in the field you'll likely need a masters anyway so will specialise then and if you want to work in an unrelated area then it won't matter much either way and I'd say it probably looks better to have a more general qualification that people can relate to a bit more.

I am studying Environmental Sciences and am thinking about specialising in chemistry. I have the option to specialise in either geology, biology or chemistry but is only indicated by which modules I choose to take and will not change the name of my degree. My worry is that of I choose to take a chemistry masters I would need to specialise in chemistry because otherwise there simply wouldn't be enough chemistry content. Not knowing exactly what I want to do and subsequently keeping the degree broad will leave me
with few options when it comes to choosing
masters because I simply won't have enough of any subject to be accepted.

That's not necessarily true, as a quick Google of environmental sciences masters can find out. If you want to do a chemistry masters, you should be doing a chemistry degree though. But you could always do an environmental sciences masters that had a large focus on chemistry. My advice would be to do the modules you think sound most interesting, until you find something you really want to do research on, and then start to tailor your degree towards doing a masters on that sort of thing.

I'm sorry, what's not necessarily true?

"keeping the degree broad will leave me with few options when it comes to choosing masters because I simply won't have enough of any subject to be accepted"