You can do PhD in the areas you mentioned. But be seriuos with your academic work and also try and do some part-time work to save some money. You need to register some amount of money to start a PhD, once you are in the system you can struggle for funding in your school. You need very good first and second degrees to get funding for PhD in UK. I completed a comparative studies in Univ of Oslo and now over half way in PhD in London. Best Wishes