I can't say I've ever had an issue with it myself - of course there are people who are right wing, perhaps more than in the population as a whole, but Durham is full of as diverse a range of viewpoints, and there are almost always people who you'll find whose views are similar to yours. Perhaps certain subjects/colleges may attract people with certain viewpoints - as an Anthropology and Sociology student, almost everyone I've encountered on my course is liberal and left-wing, which is what I would expect from a subject like that, perhaps more so than something like, Law or PPE (though bear in mind that I am generalising and making assumptions here that really aren't necessarily true). There are also societies for pretty much every main political and social viewpoint, from a Conservative Association to Green Party group and Marxist Society, as far as I'm aware. Either way, it won't be difficult to find people who hold similar, left-wing views to you, I would imagine.
(Also, as Antifazian said, it is, on the whole, a rather apolitical university generally, and the politics stuff is done far more on an individual level rather than the university as a whole)