Conservative candidate in Plymouth Johnny Mercer has hit out at the city's council after it emerged hundreds of students had been put on the electoral roll without having registered

A Labour-run council has been accused of illegally registering students to vote en masse.

Around 850 students and under-17s in Plymouth were put on the electoral roll without having completed their own applications.

Some Conservatives in the city suspect the move is an attempt to boost the Labour vote by increasing the number of young voters, who polls show tend to vote for left-wing parties.

The same council was investigated over the same issue earlier this year, when 3,000 students were said to have appeared on the electoral roll without having registered.

Johnny Mercer, the Tory candidate for Plymouth Moor View, wrote on Twitter: 'Really disappointed that, again, Plymouth City Council have registered students to vote en masse without their consent.

'I want as many people to vote as possible, but don't believe in these practices which are inevitably open to abuse, and are not legal.'

The council said 137 of the 635 students wrongly added to the register had been sent polling cards, but it has now written to them saying they have now been removed from the roll and need to re-register.

But some in the Tory party fear other councils around the country may be making similar errors.

The port city contains two battleground constituencies for the upcoming General Election

A statement by Plymouth council said: 'An issue came to light last week when we were notified that some 17-year-olds in the Plymouth Sutton and Devonport constituency had received poll cards despite not yet being eligible to vote.

'We identified the cause of the problem and have written to 247 under-18s in the Plymouth Sutton and Devonport constituency who may have erroneously been sent polling cards.

'There is no risk of them being able to vote until they are eligible as they are marked on the current electoral register as not being of age, so would not be given a ballot paper.

'As a result of this we carried out a rigorous review of the data used to compile the register. This has highlighted an issue related to some of the data we have used as part of our ongoing effort to ensure young people can vote in line with national best practice.

'The way this data is electronically marked on our electoral system has led to 850 students and young people incorrectly being added to the register.'

The statement added: 'We believe we have now identified and resolved the issues with the register. Anyone who shouldn't have been on the register has been removed, or will be in the next few days through due process. No one entitled to vote has been prevented from doing so.'

The election watchdog said it was 'disappointed' in the authority and would be 'working closely with the council to fully understand and address the issues that have been identified'.

An Electoral Commission spokesman said: 'We are disappointed that Plymouth City Council have included a number of people on the electoral register without them having made an individual application to register to vote, particularly as this was also identified as an issue ahead of the May elections.

'It's vital that electors and those taking part in elections have confidence that the register is accurate and complete, and we will be working closely with the council to fully understand and address the issues that have been identified.'