Businesswoman and campaigner Gina Miller, known for leading two successful landmark legal challenges related to the Brexit process, said she hopes that Britain's next leader will have "a plan" for the UK's future relationship with Brussels, hours after Prime Minister Keir Starmer announced he would resign.

The British-Guyanese 61-year-old became one of Britain's most divisive political figures after she took the successive Conservative governments of Theresa May and Boris Johnson to court, contesting their handling of the UK's exit from the European Union in 2016-17 and 2019.

"I'm hoping that the new leader of the Labour Party will have a plan and a strategy, some clarity on the direction of travel on our relationship with Europe," Miller told Euronews on Monday — the eve of the 10th anniversary of Brexit.

"I have been very disappointed that Prime Minister Starmer was not much clearer on what he called 'realigning'."

Although Starmer was arguably Britain's most pro-European leader since the Brexit vote, he cautiously balanced calls from within his party to strengthen the UK's ties with the EU and longstanding public opposition to challenging the referendum's outcome.