A pledge to scrap the UK's membership of the European Convention of Human Rights (ECHR) will reportedly be at the centre of the Conservative's 2020 general election manifesto, despite Theresa May previously dropping the plan.

The prime minister wants to "lift and shift" rights from the convention into UK law, according to The Telegraph.

"A clean break is by far the best option and, if we put it in the manifesto, even those Tory MPs who are squeamish about the idea will have to get behind it," a government source told the paper.

"A manifesto pledge also means the Lords will have to let it through eventually. All the signs are that the Prime Minister is up for this."

The development comes just over six months since May seemingly scrapped her previous anti-ECHR commitments.

"I've set my position on the ECHR out very clearly, but I also recognise that this is an issue that divides people, and the reality is there will be no Parliamentary majority for pulling out of the ECHR, so that is something I'm not going to pursue," she said on 30 June.

The comments were part of May's successful bid to succeed David Cameron and become Conservative leader.

The ECHR is separate to the European Union, but May – a Remain campaigner – had used a speech ahead of the EU referendum to call for the UK's withdrawal from the treaty.

"The ECHR can bind the hands of parliament, adds nothing to our prosperity, makes us less secure by preventing the deportation of dangerous foreign nationals – and does nothing to change the attitudes of governments like Russia's when it comes to human rights," she said.

But campaigners have warned that the Human Rights Act, which commits the UK to the ECHR, protects people's rights and is a legal cornerstone of Northern Ireland's Good Friday Agreement.

"The Human Rights Act protects all our rights and any attempts by this Government to erode them will be met with the most robust opposition, certainly from Liberal Democrats, but also from the other opposition parties and some on the Conservative benches as well," said Jonathan Marks, the Liberal Democrat's justice spokesman.

"Now more than ever our rights, enshrined in British law under the Human Rights Act, must be protected and upheld.

"So I would urge the Government to abandon these plans altogether and get on with trying to agree on a plan for our future relationship with our European partners."