Plans requiring voters to prove their identity before casting their ballot are deeply flawed, the Electoral Reform Society (ERS) has said.

The group said it appeared the plans were a “calculated effort by the government to make voting harder for some citizens”.

Pilot schemes will be in place at Bromley, Gosport, Swindon, Watford and Woking councils in the local elections in England on 3 May.

The ERS said personification fraud, in which someone votes while pretending to be someone else, is “incredibly rare” and the introduction of mandatory voter ID poses more problems than solutions.

The ERS chief executive, Darren Hughes, said: “It’s hard not to see this as a calculated effort by the government to make voting harder for some citizens.

“As such it’s vital we think about the risks these changes pose to a free and fair franchise in the UK. We need policy based on hard facts, not rumour and innuendo.

“With millions of people lacking the right photographic ID, and no government plans for a universal, free alternative, this can only mean another barrier for honest voters.

“The government knows this, which makes this policy all the more concerning.”

The ERS is part of a coalition of charities and campaign groups opposed to the change including Age UK, Stonewall, Liberty and the Salvation Army.

The intervention comes after a leaked letter from the Equality and Human Rights Commission said the change could have a disproportionate impact on voters from minority groups.

Hughes said: “These deeply flawed trials must not be a fait accompli for the government’s plan to roll out an ill-thought policy.

“Mandatory voter ID is a sledgehammer to crack a nut. It’s time for an evidence-based approach instead.”

In the Commons on Monday, the Cabinet Office minister Chloe Smith defended the plans and said no one would need to buy new ID documents to be able to vote.

She told MPs: “We already ask that people prove who they are in order to claim benefits, to rent a car or even to collect a parcel from the Post Office, so this is a proportionate and reasonable approach.

“Democracy is precious and it is right to take that more robust approach to protect the integrity of the electoral process.”