i am from Romania too
You will need the yellow certificate, in order to get a part-time job.
Even if we are in the European Union, we (Romanians and Bulgarians) must get this certificate.
You can check this information on the Home Office website (bia.homeoffice.gov.uk). You will see there a special section for Bulgarians and Romanians (new European Union countries).
One problem is that they do not give you exact details or requirements...everything is ambiguous.
For example, it says that you need to send them bank statements covering 3 months in the UK. The question is how we are supposed to get bank statements for 3 months, because we will arrive at the end of September and we will not have a British bank account until then. Therefore, we must wait at least 3 months after our arrival; in order apply for this yellow certificate…nice, right?
Of course, there are many other ways to get a work permit…but this is the “student” version.