Advice on postgraduate study in experimental/theoretical physics for a 3rd year Mathematics student Firstly I hope this question is appropriate to ask here. I am a third year studying Mathematics at the University of Oxford, with plans to continue to 4th year to complete the masters course.

I have been considering many paths to take so far this year, I started off by looking into finance, this I found however incredibly unintellectuality stimulating. My passions have always been for Maths and Physics, this year I will be studying quantum theory, quantum computing, special relativity and fluid dynamics, which I will continue on into 4th year with the addition of general relativity, theoretical physics and other more general applied courses.

I'm very interested in applying for a PhD after 4th year, mainly because i've never been more fascinated by the subjects i'm currently learning, Quantum theory in particular is amazing and has really changed the way I look at the universe.

Unfortunately I'm only getting a mid 2.1, however it is from Oxford so I hope that this may carry some weight, but because of this I will be mainly focusing on applying to universities other than Oxford and Cambridge.

What I'm wondering is is there any point in following this dream? I'm extremely motivated but I feel not having a first might have ruined it for me. Can anyone recommend any strategies I can use to make myself more competitive?

Currently i'm planning on applying to universities for summer research assistant placements, paid/unpaid. I'm also reading the Feynman lectures to boost my background knowledge of physics, to help bridge the gap between physics courses and my mathematics course. Can anyone recommend any other books/ideas that could help me be able to apply for experimental physics? Also universities with departments that would be good to approach.

To sum up my long and laboured question, i'm extremely passionate about mathematical physics and the idea of stopping learning about it, and say going into a deskjob is sort of horrifying. Any advice anyone can give me I would greatly appreciate.
Don't go to graduate school in physics, at least immediately.  The best case scenario is a five year program, followed by three years of postdocs, and then THAT will be followed by five years of tenure review, and THEN you might have a chance at having a stable life.  All of this happens with a tremendous amount of competition.

Use that Oxford degree to find a job somewhere for a few years, and see if you still really want to do physics at the end of that.  If you must absolutely go to school, find a terminal masters program, and learn about research some.  If you don't know whether to prefer experiment or theory, you're going to have a horrible time picking a school that has a compatible advisor, and you want to be looking for compatible future advisors far more than you want to be looking for the Platonic "quality physics programs."  So, you'll be better suited to start a PhD program effectively (and getting a masters on the way doesn't really slow you down--you are better prepared to start research after that, and the first couple of years between your quals and really starting research is where grad students flounder most frequently).  Additionally, if you are in your current situation, this will enable you to rehabilitate your academic record.  Finally, if you do your two years and don't like physics, you can find something else to do.  As someone who has finished a doctorate, I strongly recommend against immediately entering a doctoral program straight out of college.

EDIT: Additionally, as you go through school, keep some sort of exit plan--sign up for those numerical projects and learn programming.  Take the sensor analysis class and learn how to align a laser.  Learn the basics of data analysis.  There are all sorts of skills that physicists have that are wanted not just in academia, but also in the private sector or government.  Make sure that you have the skills to go out and do something enjoyable, even if it is not academic physics.  Because the odds are really, REALLY against anyone making it in academic physics (and none of these things will hurt your physics career, to say the least).