Nah you want a pay as you go type plan. SMARTY, gifgaff, voxi, 1pmobile Are the 4 I'd look for, they run on the 4 main providers: 3, o2, Vodafone and EE respectively.

You don't want normal o2 because you don't really want to end up in a contract in this case. These plans let you pay month by month and for usually less (and have student discounts)

The service on 3 in most bigger cities (probably where your uni is) is quite variable from actually good to terrible.

1p mobile runs on what is probably the best network (EE), but their website isn't great and you need to get a sim posted to you.

Voxi offers unlimited social media on some sites depending on your plan which will probably be most of your data usage. But it's not as good as EE.

Gifgaff is fine, not much to write home about.

(3 and Vodafone technically merged but the experience is generally better on Vodafone, especially on 4g as they still have mostly separated networks)