LONDON (Reuters) - The process of Britain leaving the European Union is irrevocable once it has been triggered, a government minister said on Sunday.

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

Lawyers for the government have said that, once started, the process is irrevocable, but some EU leaders say Britain can change its mind and a legal challenge to determine whether it can be reversed has been filed with an Irish court.

"People can take cases to court. My understanding is it is irrevocable and when we press the button that will go forward," Justice Secretary Elizabeth Truss told the BBC's Andrew Marr show when asked about whether Britain could reverse the process.

(Reporting by Kylie MacLellan; Editing by Mark Potter)