Is it necessary to double major with math to be considered for theor. physics grad school?

So here is my situation.

I'm an undergraduate physics major right now (second-year) at a moderately-good university. I've experienced a bit of analysis and algebra (and almost nothing in topology, which I should change), and I like it (I do study maths on my own time - I like [complex] analysis best). However, my style and preference gears me more towards physics than anything. I've experienced working under an experimental nuclear physics group for some time now, and I love it, but it has shown me that I'm probably better suited with theoretical physics. I'm not saying that because I've proven to some people to be a genius at mathematical physics [maybe I could become one :-) ], but rather because that's where my interests seem to lie.

But I've noticed something. A lot of smart students here and theoretical physics professors at various universities come from a double math & physics backgrounds (a few just from math), and I was wondering whether I should go down that same path. I've avoided it so far because I felt that with the topics I've learned on my own, I've gone more in depth and personal as compared with my classmates, and so I feel that it is in my best interest to continue to do so with my math courses. Also, I feel that getting the math degree will only take up time and my full-attention from my normally planned physics track.

On the other hand, I feel that I could probably learn quite a few things from my math classes that I wouldn't learn otherwise. Professors already know the material they're teaching, so they typically know what to teach you. On top of that, if I wanted to enter a theoretical physics program for graduate school, I might have more of a chance of being considered with that extra degree.

Does getting a double degree in mathematics and physics better increase your chances of being admitted to a graduate program in theoretical/mathematical physics?