You can register to vote if you are: 16 years old or over and a British, Irish, qualifying Commonwealth or European Union citizen who is resident in the UK (except for service voters or overseas voters who can reside abroad).
Seventeen and some sixteen year olds are able to be included on the register of electors as an 'attainer'. They will then be able to vote as soon as they are 18.
For Commonwealth citizens to be able to register to vote they must be resident in the UK and either have leave to enter or remain in the UK or not require such leave. The definition of a 'Commonwealth citizen' includes citizens of British Crown Dependencies and British Overseas Territories.
Citizens of the European Union (who are not Commonwealth citizens or citizens of the Republic of Ireland) can vote in local elections in the UK and some referendums but are not able to vote in UK Parliamentary general elections.