So I've been looking at physics courses and have decided that I would like to study theoretical physics, however a lot of universities do not offer theoretical physics courses - so I was wondering, is maths and physics a suitable alternative - or will I leave uni lacking in knowledge in both fields ? (Which is important if I want to go into research). Thanks guys, any help appreciated.
Maths and Physics shouldn't leave you too short, but the joint ones often, to an extent, leave you a bit short in the most specialized areas at least. I would personally recommend you go for either theoretical physics, straight physics or maths as opposed to maths and physics. In a straight physics degree there should be plenty of options for taking theoretical modules later on (3rd and 4th year mainly, maybe 2nd as well), likewise in maths there will often be some physics based modules for you to move into. There's no shortage of theoretical physics degrees though, so unless you're looking at a specific couple of unis that you want to go to, you shouldn't have an issue in finding one at a uni you like.
Maths and physics are close enough for you to not be losing out too much (degrees like physics and music for example are further apart so you miss out on some things), but maths degrees and physics degrees are still very different, so you wont be able to cover the whole of either. It might be worth looking up the unis with theoretical physics, and then to supplement that choice, get the core physics courses at unis you like, and have a look at the options in later years for theoretical modules.