Boris Johnson has been urged to change his plans to require voters to show ID in order to cast their ballot risk, amid warnings the plan would take a "sledgehammer to political engagement" in the country.
A group of 17 civil society groups called for the Prime Minister to drop the plans - arguing they would pull up the drawbridge for millions of voters who lack photographic ID and turn polling station workers into "de facto bouncers".
The government has argued the plans, included in the Queen’s Speech, are necessary to prevent the "inexcusable potential" for voter fraud.
However, representatives from organisations including the Electoral Reform Society, Stonewall, Liberty, Operation Black Vote and the National Union of Students called for a rethink.
They said the plans could cost £20 million per general election and 3.5 million people currently lack photographic ID.
"As the government has often made clear, voting is safe and secure in the UK – making mandatory voter ID a solution in search of a problem," the groups said.
"Instead, these proposals will turn polling workers into de facto bouncers – a role they do not want to have and which raises its own risks of discretion and discrimination.
"Our democracy is already deeply unequal, with millions missing from the electoral roll and with major gaps in turnout between groups.
"We need to be revitalising our democracy – not taking a sledgehammer to political engagement.
"Rather than inventing bogeymen and scare stories, ministers should focus on the real priorities facing our democracy."
Details of acceptable forms of ID have not yet been set out but a free council-issued “local voter card” will be available, Downing Street has said.
Officials have pointed out ID is already required to vote in Northern Ireland as well as countries such as Canada, France, the Netherlands and Sweden.
Shadow democracy minister Cat Smith said: "Ministers should heed the warnings of these respected civil rights groups, who know first-hand the undemocratic and discriminatory impact of these voter ID plans.
"Voter ID is a total waste of taxpayers’ money. The policy is set to cost millions of pounds at every election. Voting is safe and secure in Britain.
"Ministers should be promoting confidence in our elections instead of spreading baseless scare stories which threaten our democracy."
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The government does not recognise the £20 million cost put on the move by the Electoral Reform Society.
A Cabinet Office spokesman said: "In our current electoral system, there is inexcusable potential for someone to cast another’s vote at the polling station.
"Stealing someone’s vote is stealing their voice and that is why we are bringing forward legislation to stamp out the potential for fraud.
"Newly published research shows that 98% of people already have the identification required and we will work with the electoral sector and make the new requirements clear to the public in advance of elections."