A human rights deficit will be created by the government’s EU withdrawal bill, leaving many different groups in society without adequate protection, leading civil rights bodies warn in a letter published in the Observer.

The organisations spell out profound concerns that a raft of rights will be jettisoned with no adequate replacement once the bill becomes law and the UK leaves the EU.

Among others, the Equality and Human Rights Commission (EHRC), Amnesty International, Liberty, the Fawcett Society and National Aids Trust warn that the bill, which is returning to the House of Commons on 16 January, “will not protect people’s rights in the UK as the government promised”. They say: “This is in large part because the bill removes the EU charter of fundamental rights from our law.”

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David Isaac, the chair of the EHRC, the UK’s own independent human rights watchdog, said: “The government has promised there will be no rowing back on people’s rights after Brexit. If we lose the charter protections, that promise will be broken. It will cause legal confusion and there will be gaps in the law.

“While securing trade deals is vital for our economy, equality and human rights are also essential. They must also be the focus for the type of country we want to be after Brexit. Current protections must not be jeopardised.”

According to the signatories to the letter, “The charter protects rights important to all of us: including rights to dignity, protection of personal data and health; and protections for workers, women, children, and older people, LGBTI and disabled people.”

The government maintains that the charter will cease to be part of UK law when Britain leaves the EU but insists that rights will not be weakened following Brexit. However, the signatories claim that independent legal advice shows this to be wrong.

The protection afforded by the EU charter of fundamental rights is much stronger than the Human Rights Act Trevor Tayleur

“Losing it creates a human rights hole because the charter provides some rights and judicial remedies that have no clear equivalents in UK law,” they write.

“Furthermore, by keeping the wide and complex body of EU law while throwing away the charter, which is the code to unlock it, the government risks creating confusion, jamming itself in a mountain of legal cases.” According to the EHRC, rights that would be lost, and which do not have direct equivalents in other UK human rights law, include a freestanding right to non-discrimination, protection of a child’s best interests and the right to human dignity.

Keir Starmer, the shadow Brexit secretary, has said that Labour will propose an amendment to the withdrawal bill when it returns to the Commons on Tuesday, aimed at retaining the charter as part of UK law.

Trevor Tayleur, an associate professor at the University of Law, explained that the charter, although narrower in focus than the Human Rights Act, offers a more robust defence of fundamental rights.

“At present, the main means of protecting human rights in the UK is the Human Rights Act 1998,” he said. “This incorporates the bulk of the rights and freedoms enshrined in the European convention on human rights into UK law and thereby enables individuals to enforce their convention rights in the UK courts. However, there is a significant limitation to the protection afforded by the HRA because it does not override acts of parliament.

“In contrast, the protection afforded by the EU charter of fundamental rights is much stronger because where there is a conflict between basic rights contained in the charter and an act of the Westminster parliament, the charter will prevail over the act.”

Koldo Casla, policy director at Just Fair, an NGO that monitors and campaigns for economic and social rights in the UK, is one of the letter’s signatories. He said: “Britain is the land of the Charter of the Forest, the Peasants’ Revolt and the Putney Debates, the birthplace of Thomas Paine and John Stuart Mill, the country of the NHS, the home of the council house.

Social rights have been part of Britain’s tradition for centuries and Brexit should not change that. We must preserve the EU charter of fundamental rights and we must incorporate into our legal system all other social rights standards that the UK has voluntarily signed up to at the international level.”