Students studying just one subject at a British university would use the phrases in the previous post. However, it is possible to study two subjects at the same time, with the same weight given to both subjects. This is called a "Combined Honours" degree (also known as a "Dual" or "Joint" degree). It is also possible to study two subjects but for more time to be given to one subject - that is call your major subject. The other is called your minor subject.
Have a look at this page from the University of Leicester.