Theresa May’s controversial plans to withdraw the UK from the European Convention on Human Rights could be blocked by a legal challenge.

The Prime Minister is widely thought to be planning on running a 2020 election campaign on the basis of withdrawing from the ECHR in a major reform of human rights legislation.

The plans were drawn up by her predecessor David Cameron, amid concerns European laws make it too difficult for the Government to deport suspected criminals and terrorists.

In 2013, then Home Secretary, Ms May announced the Conservatives’ next manifesto would include a pledge to scrap the Human Rights Act which was introduced under Labour. She said such a move would send a message to judges who “chose to ignore Parliament and go on putting the law on the side of foreign criminals instead of the public.”

Mr Cameron’s Government backed the plan too, however he failed to enact it before his resignation. Ms May’s Government has confirmed it intends to push ahead with the proposal after Brexit. A spokesperson has confirmed a British Bill of Rights will be published following Brexit. Although, senior Conservatives are pressing Ms May to go one step and guarantee full ECHR withdrawal.

However, lawyers and campaign groups in Northern Ireland say that to do so could be a breach of the Good Friday Agreement. The Agreement is a peace treaty which ended the Northern Irish Troubles conflict and was voted on in referenda in Northern Ireland and the Republic of Ireland, before being lodged as a treaty to the UN. Critics say withdrawal from the ECHR would breach the treaty by removing avenues for justice and reconciliation for people affected by the conflict.

Stewart Dickson, a member of the Northern Ireland Assembly, told The Independent that lawyers, politicians and victims’ groups supporting those affected by The Troubles “will be queuing up to take legal action” to block the plans.

He said: “There is anger about attempts to scrap the Human Rights Act. I have little doubt there will be a legal challenge. There are a slew of actors queuing up to take action. It could be taken by one or more political parties, a group of activists, victims or others. Anyone affected by the Good Friday Agreement and how it links to human rights legislation could do it. There are ample opportunities here.”

Fiona De Londras, Professor of Global Legal Studies at the University of Birmingham, echoed his warning, telling The Independent: “Withdrawal would almost certainly result in a breach of the Agreement as currently framed and understood, and is certainly well beyond what was contemplated when the Agreement was reached and approved by referendum.”

She explained: “I would imagine that a legal challenge is likely to any proposed withdrawal from the ECHR on the basis of an alleged breach of the Good Friday Agreement, although much may depend on what if anything the Supreme Court says about the constitution of Northern Ireland in the Brexit case, the judgement in which we await. That will largely determine likelihood of taking a challenge and of its success.”

The Supreme Court is currently hearing a legal challenge to May’s plans to trigger Article 50 thereby sparking negotiations to leave the without allowing MPs to vote on it first. Judges were told Northern Ireland will be adversely impacted by Brexit and so Northern Ireland must approve triggering Article 50, in addition to Westminster MPs, by approving a legislative consent motion.

Withdrawing human rights protections became a key challenge for Ms May after her tenure as Home Secretary was undermined by repeated failed attempts to deport Abu Qatada, a radical Muslim preacher. Nearly a decade of appeals, involving expensive legal battles, occurred before she succeeded in deporting him due to human rights legislation.

Professor De Londras also told The Independent that withdrawal from the ECHR could also prompt further insecurity in Northern Ireland in potentially influencing whether local people wish to remain part of the UK. She said: “Should the people and political system of Northern Ireland determine that withdrawal from the ECHR is a serious rupture in the agreed constitutional settlement in Northern Ireland this may result in calls to revisit Northern Ireland’s continuing presence within the United Kingdom. Should that happen, the fragility of the peace in Northern Ireland would certainly be a matter of concern.”

The European Court of Human Rights is an international body established by the European Convention on Human Rights. Individuals and groups can lodge complaints with the court to allege that a signatory state breaches any of the human rights stipulated in the Convention. The 47 member states of the Council of Europe (which includes the UK as a member) are signatories.

In April of this year, while serving as Home Secretary prior to becoming Prime Minister, Ms May said: “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.” It is believed she intends to “list and shift” ECHR human rights stipulations into UK law by creating a new ‘British Bill of Rights’.

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However, critics have warned that a British bill would be effectively pointless if the UK remains bound to the ECHR. Senior Conservative figures are said to be pushing for full ECHR in order to avoid such a scenario.

Mr Dickson said his party, which is a cross-community party formed to tackle sectarianism in Northern Ireland, will also seek to block the plan through a vote at Stormont. He said ECHR withdrawal should require a vote in the regional, devolved assemblies in Northern Ireland, Scotland and Wales, called a legislative consent motion, which allows them to approve or block central government plans. He said Alliance would also vote against such a motion, meaning it is likely the policy could be blocked. He said: “You can be absolutely sure Alliance would oppose it and indeed anything which undermines human rights laws.”

Mr Dickson said the party could even employ a petition of concern, a mechanism in Northern Irish power sharing structures which can allow parties to effectively block legislation. It is a controversial practise which the Democratic Unionist Party have famously used to block passing same-sex marriage on multiple occasions. However, Mr Dickson said using a petition of concern to block ECHR withdrawal “would be absolutely justified”.