Nearly four million people could be stripped of the right to vote in local elections if Britain crashes out of the EU without a deal.
The Government has confirmed almost half a million British people living in the EU, plus another 3.5 million EU citizens living in the UK would be blocked from casting their vote.
Liberal Democrat Brexit spokesman Tom Brake revealed the information through a parliamentary question on reciprocal voting rights, which have only been secured with Spain, leaving millions more potentially unable to vote next month.
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In a written response, Brexit minister Robin Walker said: "The UK pushed for reciprocal rights to stand and vote in local elections in negotiations on citizens' rights but they will not form part of the Withdrawal Agreement.
"Instead we are pursuing bilateral agreements with individual Member States where possible, to apply in a deal or no deal scenario.
"We are pleased to have secured the first such bilateral agreement on local voting rights with Spain in January and we are continuing our discussions with other Member States."
Mr Brake said the response showed how Brexit was "tearing democracy apart" due to "callous Conservative Party self-interest".
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He said: "Far from illusions that Brexit would renew our democracy, it is instead tearing it apart and stripping people of their rights all because of Tory incompetence.
"Many EU citizens fill vital roles in the health service, our schools and across Parliament. They deserve better, and the Liberal Democrats demand better.
"The upcoming local elections are therefore an opportunity to send a clear message to Theresa May and Jeremy Corbyn's failed leaderships by voting for the Liberal Democrats.
"Every Liberal Democrat elected in May is another voice fighting for a People's Vote, with the option to stay in the EU."
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Campaigners for EU citizens in the UK, the3million, said the potential loss of rights in May came on top of EU citizens being left without a vote in the 2016 referendum.
Ilse Mogensen, public affairs and campaigns officer for the3million, said: "EU citizens living in the UK were denied a vote on our own future in the 2016 referendum.
"To add insult to injury, we now face the loss of our right to vote and stand as candidates in local elections.
"The Welsh and Scottish governments have confirmed that EU citizens will keep the right to vote - the UK Government should do the same, instead of leaving the democratic rights of 3.6 million people in limbo."
