Who is eligible to vote at a UK general election?

from Election Commission website

You can register to vote online from anywhere in the UK at here.

To vote at the UK general election you must be registered to vote and:

• 18 years of age or over on polling day
• be a British, Irish or qualifying Commonwealth citizen (‘qualifying’ Commonwealth citizens must have leave to remain in the UK or do not require such leave)
• be resident at an address in the UK (or a UK citizen living abroad who has been registered to vote in the UK in the last 15 years)
• not be legally excluded from voting

The following cannot vote in a UK Parliament election:

• members of the House of Lords
• EU citizens (other than UK, Republic of Ireland, Cyprus and Malta) resident in the UK
• anyone other than British, Irish and qualifying Commonwealth citizens
• convicted persons detained in pursuance of their sentences, excluding contempt of court (though remand prisoners, unconvicted prisoners and civil prisoners can vote if they are on the electoral register)
• anyone found guilty within the previous five years of corrupt or illegal practices in connection with an election
  

  Who can register as an overseas voter?

If you are a UK citizen living abroad, you can apply to be an overseas voter.

You must have been registered to vote in the UK in the last 15 years and be eligible to vote in UK Parliamentary general elections and European Parliamentary elections.