A number of Green Party leaders in Britain and Northern Ireland have been named as plaintiffs in a case before the High Court in Dublin to establish if Britain can halt Brexit after it triggers article 50 of the Lisbon Treaty.

Lawyers will file a plenary summons to start proceedings on Friday, hoping for a hearing in March or April.

Jonathan Bartley, co-leader of the Green Party of England and Wales; Northern Irish Green Party leader Steven Agnew MLA; and the Green Party MEP for the South East of England, Keith Taylor, will join Jolyon Maugham QC, a leading British barrister, as litigants in the case.

They are seeking a referral from the High Court to the European Court of Justice of the European Union to determine whether article 50, once triggered, can be unilaterally revoked by the UK government without requiring consent from all other 27 EU member states.

Mr Bartley said the case was about giving people in the UK a legal safety net after Brexit negotiations begin and to offer clarity about whether Britain can change its mind if the negotiations go badly.

“The government claims that it can’t revoke article 50. But if it is wrong, the British people would have a safety net that could allow them a real choice in a referendum on the terms of the Brexit deal. They would be able to choose between accepting Theresa May’s vision of extreme Brexit or rejecting it.”

Authorisation of parliament

Britain’s supreme court ruled this week that Ms May cannot trigger article 50 without the authorisation of parliament at Westminster. The court said, however, that the devolved administrations in Belfast, Edinburgh and Cardiff had no such veto, and did not have to be consulted.

“The unique status of Northern Ireland is being ignored with our traditional parties involved in local squabbles. Any deal on the Irish Border will have massive implications across the island and it is vital that the people of Northern Ireland have a say on the final proposal,” Mr Agnew said.

“For that to be meaningful, the option to remain must still be on the table. Otherwise, the UK has no leverage in article 50 negotiations, as the current assumption is that if we like the Brexit deal, we leave, and if we don’t like it, we leave anyway. Only if this case is successful will the UK have a choice, which is why I believe that this case should be welcomed by all UK citizens whether they voted leave or remain.”

Mr Maugham is funding the action through a crowd-funding exercise which reached its target of £70,000 (€82,000) within two days, largely from small donations. Mr Maugham said he respected the referendum result and agreed that article 50 should be triggered, as planned, but it was important that Britain should have the option of remaining in the EU if circumstances or public opinion change.

“Establishing that the article 50 notification can be revoked gives us a free option in an uncertain world. Whether to exercise that option is for the electorate. But no one can deny that our national interest is served by us having it,” he said.