Haha, your experiences sound a lot like mine xD I'm currently rolling on 5th year of undegrad due to changing universities, programmes and having a breakdown forcing me to take 3 quarters of a year out xP
Anyhue, your stats sound pretty solid tbh. They'll definitely want to hear about your thesis thought (you should make sure you're comfortable talking about it and the subject matter generally for interviews if you do apply), and getting Bs in "advanced" maths courses probably won't hurt your chances too much (well, maybe for part III maths or QFFF, but part III physics or any of the other physics courses at imperial you should be fine, and for phd's they'll just make sure you know the stuff you need to and don't really care beyond on that).
With regards to the hating memorization, you'll probably feel at home in a UK programme, as they definitely emphasise a more conceptual approach to rote memorization (at least for undegrad). One of my friends actually managed to get full marks for a question on his advanced math methods final by basically saying "I'm not going to compute this horrible integral, because it'll take 10 pages to do so, and all the relevant physics is outside the integral and by inspection the integral is some value between 0 and 1. So essentially the answer is *blah* with a damping coefficient in front, which physically means *blah*." Although the marker for that paper was possibly more generous than some :P
Plus the approach for PhD stuff is basically "you can look in whatever books you want for equations and compute all the integrals in MATLAB you want as long as you understand the physics" from what I hear. Although apparently the Russian supervisors are a little more...intense (also the one Indian Prof we have is apparently completely insane according to my flatmate). The UK undergrad physics pedagogy is very much focused on developing physical intuition, and then developing the relevant mathematical tools as necessary (compared with the french/russian way of teaching them 2 years of pure maths and then showing the physics from that). And you can't really memorize intuition :P [Also the IOP requires all physics undegrad programmes have a synoptic paper/general problems exam which can ask questions from any area of the undergrad physics and are generally designed to require more creative problem solving and original thought to solve (you can't just write down the relevant equations and substitute all the numbers in), so there's that.]*
Anyway, I digress. From the sounds of it, applying wouldn't hurt and you have a resonable chance of at least getting interviewed.
*not 100% sure if this is an actual requirement or just a common occurrence, I haven't read the IOP specifications, but at the very least Southampton, Exeter and Cambridge have this.