Voters are at risk of being left off the electoral register ahead of next year's assembly election, the Electoral Commission has warned.

The UK government has brought forward a deadline to complete the move to a new voter registration system from December 2016 to this December.

As of May, 70,000 Welsh voters had not been transferred, the commission said.

A UK government spokesman said the claims were "nonsense" and "nobody will lose their right to vote".

Voters who have not been processed when the deadline passes will be taken off the electoral roll and must re-register.

Speaking to BBC Wales' Sunday Politics programme, Phil Thompson, head of research at the Electoral Commission, said: "Our view was this is a risk - you're taking people off the register in December who are still eligible to vote and if you take them off you're putting the onus on them to re-register before that set of polls.

"We were disappointed with the decision, we've made a clear recommendation it should remain as 1 December 2016."

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But the government spokesman said: "Individual electoral registration brings us into line with every other serious democracy in the world.

"It means that we can prove electors are genuine for the first time, and dramatically reduces the risk of electoral fraud.

"We have already confirmed 96 out of every 100 voters as genuine on the register. By the end of this year, the rest will have been contacted nine times.

"The chances of them being genuine voters, as opposed to 'ghost' entries of people who have moved, died or were registered fraudulently, is vanishingly small."

In his conference speech last week, Labour leader Jeremy Corbyn accused the Conservatives of attempting to influence the results of next year's polls by forcing voters to re-register.

"They want to gerrymander electoral boundaries across the whole country by ensuring the new, reduced house of commons boundaries will be decided on the basis of the missing millions from the voters' register," he said.

The chairman of the Welsh Conservatives and former Tory MP Jonathan Evans said the current voter registration system is "flawed" and needs to be changed ahead of next year's elections.

He said: "I've had through my letter-box more than three or four communications from the Electoral Commission outlining how this system is changing and we don't need to delay for a further year."

Mr Thompson said the deadline was changed in the knowledge the boundary commission would use data gathered from the electoral roll in December as a basis for its work when it begins reviewing constituency boundaries next spring.

Canvassing is under way to reduce the number of voters affected.