A person is entitled to be registered as a parliamentary elector if he or she is resident in the relevant constituency, is of voting age, is not subject to a legal incapacity to vote (age apart), and is either a British citizens, a qualifying Commonwealth citizen or a citizen of the Republic of Ireland.
As explained in my answer on 18 March 2009, Official Report, columns 1214-5W, under the Representation of the People Act 1983, "qualifying Commonwealth citizen" is defined as a Commonwealth citizen who either does not require leave to enter or remain under the Immigration Act 1971 or who does require leave, but for the time being has any description of such leave. This means that if a person who requires leave to enter or remain has been granted leave to enter or remain then he or she will be deemed to be a qualifying Commonwealth citizen.
Commonwealth citizens who have leave to enter or remain will have been granted this leave under any of the current or previous categories of the immigration rules, including as the spouse of a British Citizen, as a highly skilled migrant, work permit holder, student, under any of the new points based system categories or as dependants of any "lead" migrants granted leave under these categories.
This will include a citizen from a Commonwealth country who has obtained leave to enter or remain under the previous immigration rules relating to students, or since 31 March 2009, leave to enter or remain under tier 4 of the points based-system. Accordingly, provided they meet the other criteria for registration set out above, such a person would be entitled to be included in the register of parliamentary electors.