Government plans that will force people to prove their identities at polling stations in May’s local elections risk disenfranchising members of ethnic minority communities, according to a leaked letter to ministers from the equality and human rights watchdog.

In a move that will fuel controversy over the treatment of migrants in the UK following the Windrush scandal, the Equality and Human Rights Commission (EHRC) has written to the Cabinet Office minister David Lidington, raising its serious concern that the checks will deter immigrants and others from participating in the democratic process.

The Labour leader Jeremy Corbyn said the plan for compulsory checks was more evidence of the kind of “hostile environment” that Theresa May’s government wanted to create for people who had come to settle in Britain. In a speech on Sunday, Corbyn will claim that Theresa May’s determination to cut immigration at all costs was responsible for the Windrush scandal. He will say: “British citizens who came to our country to rebuild it after the war have faced deportation because they couldn’t clear the deliberately unreachable bar set by Theresa May’s ‘hostile environment’ for migrants.”

Under the new government voting rules, being trialled in several local authorities at the 3 May local elections, people will be asked at polling stations to produce documents proving their identity – such as a passport or driving licence – before casting their vote. Currently, no such proof is required.

The Windrush scandal has highlighted how many who came to this country from the Caribbean, mainly in the late 1950s, have struggled to prove their British citizenship because the authorities failed to register them or destroyed their landing cards, or because they have never applied for documents such as passports.

Ministers say the pilot projects are being run – with a view to adopting them nationwide if they are successful – in response to concerns about electoral fraud.

But in a letter to Lidington, and leaked to the Observer, the EHRC says evidence of supposed fraud is minimal and warns that there is a real risk that legal residents who might not have a passport or driving licence – or might be reluctant to produce them at polling stations – could be disenfranchised as a result.

In the letter, the EHRC’s legal officer, Claire Collier, tells Lidington: “The Commission is concerned that the requirement to produce identification at the given local elections (Bromley, Gosport, Swindon, Watford and Woking) will have a disproportionate impact on voters with protected characteristics, particularly older people, transgender people, people with disabilities and/or those from ethnic minority communities. In essence, there is a concern that some voters will be disenfranchised as a result of restrictive identification requirements.”

Reacting to the news, the Labour leader Jeremy Corbyn said: “Forcing voters at election time to prove their identity at polling stations by producing official documents would have a disproportionate impact on people from black and ethnic minority communities.

“It is the same hostile environment all over again, shutting our fellow citizens out of public life, treating communities who made Britain their home as second-class citizens. It’s disgraceful and it must be brought to an end.”

Kunle Olulode, the director of Voice4Change England, a civil society charity that has worked with the government to improve the participation of BME communities in elections said: “We feel strongly that this type of policy will not only have minimal impact on the miniscule level of voting fraud but will create potentially new and unnecessary barriers to participation in the electoral process if people become uncertain of requirements when they turn up at polling stations, further impacting negatively on registrations. Asking for voters IDs as a policy certainly has echoes of the strategy aimed at making society an uncomfortable place for illegal migrants.”

A Cabinet Office spokesperson said: “We already ask that people prove who they are in order to collect a parcel from the post office, rent a car, or travel abroad.

“We believe it is right to take the same approach to protect voting rights. Local authorities are implementing equality impact assessments and are working with partners to ensure that voter ID does not risk preventing any eligible voter from voting. It is in nobody’s interest that any elector is disenfranchised.”

Last night John Sentamu, the archbishop of York, called for an inquiry into immigration policy and the Windrush scandal in which up to 50,000 mostly Commonwealth migrants are facing problems securing their citizenship, access to healthcare and other services because of Home Office demands to see proof of their rights to be here.

“The truth is now out. Hard-working, tax-paying immigrants who were invited to this country to help with postwar reconstruction have been treated appallingly,” he told the Observer. “It is never too late to repent, but it is unwise for penitents to boast about their achievements. Instead, the government needs to set up an inquiry urgently to discover where other aspects of our immigration policy are treating people as less than human.”

It has also emerged that the “hostile environment” for illegal immigrants was implemented despite warnings from a Tory cabinet minister that it would lead to exploitation and endanger health.

Investigations show that the plan to force landlords to check the immigration status of tenants, known as the “right to rent”, was fiercely opposed before its implementation by Eric Pickles, the former communities secretary. In an internal memo written in February 2013, he warned: “It would be disproportionately burdensome, ineffective and intrusive to oblige all private landlords to satisfy themselves as to the immigration status of prospective tenants. It’s hard to assess how many illegal immigrants this policy would deter in practice as it would be easy to circumvent/evade detection.

“Those landlords/agents who are already rogues will not obey the law – and will make more money by exploiting a niche market in illegal tenants by increasing rents/compromising on health and safety for tenants who cannot complain ... The costs and risks considerably outweigh the benefits.”

Amber Rudd, the home secretary, appeared to blame her department for the Windrush scandal last week, saying: “The Home Office has become too concerned with policy and strategy and sometimes loses sight of the individual”.

Facebook Twitter Pinterest Amber Rudd appeared to blame her officials for being ‘too concerned with policy and strategy and losing sight of the individual’.

Photograph: Niklas Halle'n/AFP/Getty Images

However, Brodie Clark, the former head of the UK Borders Agency who resigned after being criticised by May in 2011 for relaxing passport checks to reduce immigration queues, condemned the decision to blame officials and pointed to a “political desperation” to reduce immigration.

“In my time with UKBA, I had the greatest regard for frontline staff and their ability to do their jobs effectively,” he said. “They saw their job as defending the country, but doing it in a fair and decent fashion.”

“To hear any political leader now saying, ‘The trouble is, they were too obsessed in delivering policy and not enough about caring for people’, just beggars belief. Civil servants are employed to deliver government policy and deviation is certainly not rewarded. It is a shameful shot, given the dedication, commitment and skill of those staff.”

The National Landlords Association, the Residential Landlords Association and the lettings agents’ body ARLA Propertymark are all pushing for the “right to rent” policy to be dropped amid warnings that it is causing landlords to discriminate against people with foreign names or non-UK passports. The policy was piloted from December 2014 and rolled out across England in February 2016.

A Downing Street spokesman said: “It was a Labour government which, in 2008, introduced the labour market test so that people had to evidence their status. And it is fair that only those who have a right to be here can work legally, rent property and access public services.”