You'll do very little 'headline' Physics as part of your course, by which I mean things like QED and String Theory, the vast majority is nuts and bolts stuff like optics, electromagnetics, statistics, and mathematics. Normally with the word 'applied' in front. Quantum Mechanics is much less fun than it sounds anyway.
In the end I loaded up my last two years (I was Mphys) with computational physics and medical physics electives and tried to avoid as much of the nasty algebra as possible. Personally I found the practical lab work (fiddly optics stuff with lasers
) to be a godsend because it had a big percentage of the final years marks and I scored pretty highly.
Physics may offer a slightly wider range of possible careers after graduation than computer science, although a lot of employers only make the distinction of a 'numerate degree' and go by application form and interview.
Beyond the degree phase there are plenty of areas of Physics research where hefty computing power is employed and often multidisciplinary teams of programmers and physicists are employed.
In short choose the course you have the most enthusiasm for as it will dominate your life for at least three years. If you think you've got it wrong at the end you can always do a 1 year masters and requalify.