LONDON (Reuters) - A crowdfunded legal challenge to determine whether Britain’s divorce from the European Union can be reversed once it has been triggered will be launched in Dublin by the end of January, the lawyer behind the case said.

People hold banners during a 'March for Europe' demonstration against Britain's decision to leave the European Union, in central London, Britain July 2, 2016. REUTERS/Neil Hall

British Prime Minister Theresa May says she will invoke Article 50 of the EU’s Lisbon Treaty by the end of March, triggering two years of formal divorce talks.

Lawyers for the British government have said that, once started, the process is irrevocable, but some EU leaders say Britain can change its mind.

Jolyon Maugham, a London tax lawyer, is taking legal action to seek a ruling from the European Court of Justice on whether Britain can unilaterally revoke Article 50 without the consent the other 27 EU states.

He said “a letter before action” would be issued against the Irish state on Friday and that legal proceedings would begin in Dublin’s High Court on or before Jan. 27.

“If we change our minds we must be able to withdraw the notice without needing the consent of the other 27 Member States,” Maugham said in a statement.

He said the challenge, in which several unnamed UK politicians would act as plaintiffs, would also seek clarification of what rights they would lose as EU citizens when Article 50 was triggered and when they would lose these rights.

Their case is that Britain’s exclusion from EU Council meetings since the Brexit vote would in contravention of European treaties unless Article 50 had already been triggered.

“This is really important stuff, not just for the United Kingdom but for the whole European Union … our politicians really ought to know the legal framework in which they are operating,” Maugham told Irish broadcaster RTE.

Maugham, whose supporters raised 70,000 pounds ($90,000) in 48 hours last month to fund their challenge, told Reuters in an interview in December that his case would not stop Brexit but would allow for a change of heart if Britons who voted to leave the bloc had a change of heart.

Britain’s Supreme Court is expected to rule in the next couple of weeks on whether May can trigger Article 50 without parliament’s approval or the assent of devolved assemblies in Northern Ireland and Scotland.

Next week London’s High Court is due to hear a challenge on whether leaving the EU means Britain automatically leaves the European Economic Area (EEA) which allows access to the single market and free movement of goods, capital, services and people.