Government attacks on human rights legislation were condemned last night as an “unhinged” betrayal of British values, destined to destroy the country’s reputation on the world stage.

As the Home Secretary and Justice Secretary separately threatened to draw back from the European Court on Human Rights, the Conservative Party was accused of being in disarray and caving in to the right after its humiliating defeat in the Eastleigh by-election.

Leading lawyers and human rights advocates said ministers risked making the UK a pariah state alongside Belarus – the only European country that has not signed the European Convention on Human Rights. On a day when David Cameron claimed there would be no “lurch to the right” in the wake of the Eastleigh result, both Chris Grayling and Theresa May were accused of pandering to the far right of their party.

In conflicting statements, Mr Grayling indicated the Tories would abolish the Human Rights Act in the UK while it was reported that Ms May wanted a pledge in the next Conservative manifesto to withdraw from the European Convention on Human Rights altogether.

Shami Chakrabarti, director of Liberty, said: “Churchill must be spinning in his grave as modern Tory Cabinet ministers trash his post-war legacy.

“They can’t even seem to agree on whether it’s the Human Rights Act or European Convention they want to scrap.” Both ideas are currently being blocked by the Liberal Democrats from becoming Government policy.

Only Belarus has not signed up to the landmark ECHR treaty, drawn up in the aftermath of the Second World War, largely at the behest of Winston Churchill.

The leading human rights barrister Ben Emmerson QC accused the two ministers of working in a political pincer movement: “The increasingly shrill rhetoric from Theresa May is beginning to sound decidedly unhinged. There is not the slightest prospect of the UK pulling out of the European Convention before the next election.”

“In Europe and the UN the UK is seen as having lost the plot. The UK’s international reputation as a leader on the rule of law and human rights is plummeting at an alarming rate and with it our ability to influence other states. I cannot recall a time since 2003 when the UK’s international reputation has fallen farther and faster.”

His comments were echoed by Amnesty International’s UK director Kate Allen, who said the “drumbeat of threats” was proving hugely damaging to the UK’s reputation.

“Instead of throwing their toys out of their prams like this, government ministers should be seeking to improve the workings of the Strasbourg court where they can. Most of all, Britain should be a strong advocate of a convention that rightly outlaws torture and unfair trials everywhere from Vladivostok to Galway,” she added.

The Government has been at loggerheads with Strasbourg over a series of judgments, including blocking the deportation of the radical cleric Abu Qatada and ruling that some prisoners must be given the vote. The outgoing President of the European court, Sir Nicolas Bratza, recently described his disappointment that the ECHR had become a “hate figure” in his own country, despite the fact that just three per cent of cases from the UK were even considered admissible and just half of those succeed.

But today Mr Grayling indicated the Tories would repeal the Human Rights Act – which enshrines the Convention in British law – if they won the next general election with a majority. “I cannot conceive of a situation where we could put forward a serious reform without scrapping Labour’s Human Rights Act and starting again,” he said. “We need a dramatically curtailed role for the European Court of Human Rights in the UK.”

Meanwhile it was reported that Mrs May is set to announce plans to withdraw from the convention altogether before 2015, a move that has been vociferously opposed by the Liberal Democrats.

Yesterday a senior Government source played down suggestions that Britain might opt out of the European Treaty altogether: “I think what we’re looking at is the role that the Supreme Court should play in being the final arbiter under the law – not pulling out of the Treaty.” Pointing out that the Attorney General, Dominic Grieve, had already warned against the UK defying the European court’s judgments, Mr Emmerson urged the Prime Minister not to let UKIP and “little Englanders” dictate policy: “May and Grayling, and the people who are supporting them, are the barmy brigade of the Conservative Party. They are undermining the Foreign Secretary’s attempts to portray the UK as pursuing an ethical foreign policy and they are undermining the Prime Minister’s standing with the international community.”

A Labour spokesman added: “It’s clear David Cameron’s response to his disastrous result in Eastleigh is a lurch to the right. He is a weak Prime Minister who is caving in to the demands of the right-wing MPs in his party.”

ECHR rulings: Enlightened judgments

October 1981: The court found Northern Ireland’s criminalisation of homosexual acts between consenting adults was a violation of the convention, following a case brought by Jeff Dudgeon. As a result, male homosexual sex was decriminalised in October 1982.

September 1995: A judgment on the Death on the Rock case, condemning the SAS killing of three IRA terrorists planning a bombing in Gibraltar. The court ruled soldiers acted proportionately but condemned the authorities.

September 1998: Found that the beating of a boy with a cane by his stepfather was not “reasonable chastisement”. As a result, the Government announced that it would give children better protection.

December 1999: Ruled in favour of two gay servicemen, finding that discharge from the military was in breach of their right to a private life.