The information requested falls within the responsibility of the UK Statistics Authority. I have asked the authority to reply.
Letter from Glen Watson
As Director General for the Office for National Statistics, I have been asked to reply to your Parliamentary Question asking the Deputy Prime Minister how many registered voters there are who are (a) Commonwealth and (b) Irish but not British citizens (193520).
ONS does not hold information on the number of Commonwealth or Irish citizens registered to vote in UK elections.
ONS produces electoral statistics showing the total number of people registered to vote in local government, European parliamentary elections, and general elections. Although this total includes British citizens, Commonwealth citizens and citizens of the Republic of Ireland, data on the citizenship of registered voters are not collected.
The latest UK electoral statistics are for