British citizens living outside the UK are allowed to continue voting in the UK for a maximum of 15 years. After this point they become disenfranchised, but retain their citizenship.
The 15 year period has been shorter and longer and is set at the discretion of Parliament. The limited period of enfranchisement is intended to reflect a disconnection of overseas elector with the UK.
Article 25 of the International Covenant on Civil and Political Rights (ICCPR) states that “Every citizen shall have the right and the opportunity … To vote and to be elected at genuine periodic elections which shall be by universal and equal suffrage and shall be held by secret ballot, guaranteeing the free expression of the will of the electors”. The UK ratified the ICCPR in 1976, but continues to ignore its commitments to expatriate citizens by disenfranchising them after a 15 year period of non-residence.
Expatriate citizens are still citizens. Simplifying the Representation of the People Act 1985 by removing the time limit on expatriate enfranchisement would simplify the law and protects the political rights of overseas voters.