Publicity campaign begins to highlight voting changes
A publicity campaign is under way in England and Wales to alert people to changes to the way they register to vote.
Everyone entitled to vote must now register individually rather than - as in the past - being listed on a form filled in by one member of a household.
The Electoral Commission said 80% of those on the electoral register would automatically move onto the new system.
But about 10 million people will need to re-register.
Parliament approved the switch to individual voter registration last year and election officials across England and Wales are now writing to everyone entitled to vote to tell them about the changes, backed up by TV, online and poster advertising.
The introduction of individual voter registration is being delayed in Scotland until after the referendum on its constitutional future on 18 September.
Officials say no-one who is already on the electoral register is at risk of falling off it before the 2015 general election.
About 40 million people will receive a letter informing them of the changes but letting them know they do not need to do anything.
However, about 20% of people who have registered to vote in England and Wales will be told they need to re-register because they have not had their identity confirmed as part of a process in which election officials are "matching" details held locally with information held centrally by the Department for Work and Pensions.
Many of these people are likely to be students and others who have moved frequently in recent years. All of them will be sent letters telling them what they need to do and reminding them they can provide the information required online.
Officials will also be writing to those households where they have no information about who lives there and sending them a "household inquiry form", asking people to return details to their local council.
There are six million people in the UK who are entitled to vote but are not currently registered. In future, they will be able to register online.
"The way we all register to vote is changing in England and Wales," Jenny Watson, the Electoral Commission chairman, said.
"It is important everyone looks out for a letter from their local council that will tell you if you need to do anything."
She said individual electoral registration was an "important step towards a more modern and secure electoral system".
She added: "Online registration also helps organisations working with us and others run innovative and exciting voter registration drives that should appeal to young people in particular."
Earlier this year, a Labour MP accused some councils of taking a "lackadaisical" attitude to updating voters' records.
Council officials are supposed to go door-to-door to make sure voter lists are as accurate as possible but five councils failed to meet the watchdog's standards last year.