Most EU nationals (except Romania and Bulgaria) are allowed to work in the UK while studying. However if you are not an EU national, you are not allowed to work in any capacity whether employed or self-employed. Unless your visa expressly says you can, do not work while in the UK, if caught it can void your visa and result in deportation, and not completing your qualification.
However if you are allowed to work, this could prove to be beneficial, as you would be able to earn a little extra to keep you going while you study, as well as gaining valuable working experience and boosting your CV. However consult with the UK Council for International Student Affairs because there are a few things that will need to be taken into consideration while you are working suck as taxes and national insurance contribution.
Firstly secure whether or not you are allowed to work. If cleared, determine if there is a cap on the amount of hours you are allowed to work per week and make sure you stay within that range. Exceeding it can end up making your feel more tired and unable to focus on your study. You can find out if you are allowed to work in the UK by visiting the UK Border Agency website.
If your course involves a placement or work experience period that is compulsory to your qualification, your university should advise you on how to handle this matter in regards to your visa. When searching for a placement, you can either do this through your university, search independently or you can sign on with a recruitment agency that will help you look for work. If you decide to search through the university, you can contact the on campus careers adviser to help you.
Volunteering or unpaid work is a little bit of a grey area when it comes to working in the UK because in essence you are donating your time and not earning a wage out of it. There are many reasons why you might want to volunteer for unpaid work, a few of which could be:
Ere on the side of caution and always double check with the UK Border Agency, this is to ensure that you are not being exploited by the organization that you are donating your time to or that you may end up accidentally being in breach of your visa.