Tens of thousands could miss out on vote, watchdog warns
Tens of thousands of people could miss out on a vote in the EU referendum and May's Scottish, Welsh and English local elections after changes to the registration process.
At least 770,000 names have been removed from the electoral register, the Electoral Commission says.
The watchdog said young people had been hit the hardest.
The government says the new system will cut down on electoral fraud and "ghost" entries on the register.
Voters now have to register as individuals rather than by household.
Millions of people were transferred automatically on to the new register after having their identity confirmed by checking social security and council tax records.
Names that could not be verified in this way were kept on the register until 1 December but have now been removed.
Since December, 1.3 million people have signed up to vote individually, following an advertising campaign encouraging people to get on the electoral roll in time for May's elections in Scotland, Wales and Northern Ireland and council ballots across England.
But the Electoral Commission and the Labour Party said the transition had been rushed and people in short-term rental agreements, often in urban areas, and those moving on a regular basis, such as students, had been disproportionately affected.
Under the old system, universities registered students en masse.
The Electoral Commission said last June that 1.9 million names had disappeared from the register across England, Scotland and Wales as a result of the changes - although it was not clear how many of these were actually entitled to vote.
The government ignored the watchdog's advice to keep names on the register for longer to allow councils more time to check them.
In its latest assessment, the commission has "significantly" reduced its estimate of the missing names to 770,000 - although the figure is still equivalent to 1.7% of the total 43.4 million electorate.
But it also pointed out the figure was not comprehensive as the London borough of Hackney could not provide accurate information.
"It is not possible to estimate the number of eligible electors who were removed from the registers," it said in a statement.
"However, the commission reports that it is likely that some of the removed entries related to electors that were eligible to remain registered to vote."
It said the number of under-18s - so-called "attainers", qualifying to vote during the registration period - had fallen by 40% since March 2014.
In its report, the watchdog has made a number of recommendations to government to try to halt the decline in registration.
Labour said the decline in the number of young people registering to vote was "shocking", adding: "What's worse is that the government are shamelessly taking this as an opportunity to redraw constituency boundaries based on an electorate that is far lower than it should be."
The independent Boundary Commission for England said on Wednesday it had begun redrawing the map of parliamentary constituency boundaries in England.
The move follows a decision by Parliament to reduce the number of constituencies in the UK from 650 to 600, and to ensure that there are roughly the same number of electors in each constituency.
Sam Hartley, secretary to the Boundary Commission for England, said: "Once we publish our initial proposals in the autumn, we will need the help of residents in all regions to ensure that our proposals take account of local ties and best reflect the geography on the ground. Everyone's views will help us recommend a well-considered and practical set of constituency boundaries in England."
John Penrose, Minister for Constitutional Reform, said: "Councils have only removed 'ghost' electors - people who have moved, died or never existed in the first place - so keeping them on the register when we know they shouldn't be there, and then sending them all poll cards on election day, would be wrong, expensive and increase the risk of fraud.
"Equalising the size of constituencies in the Boundary Review means everyone's vote will carry equal weight.
"If we let some constituencies stay smaller than others, voters will have more power in them than people in bigger ones. And the boundaries would be based on data that's 20 years out of date. That can't be fair or right."
Separate figures from the Office for National Statistics suggest 600,000 people have fallen off the register in the past year.
The ONS said the total size of the UK electorate was 44,722,004.