LONDON -- Cracks in Britain's political party system yawned wider Wednesday, as three pro-European lawmakers quit the governing Conservatives to join a newly formed centrist group of independent legislators opposed to the government's conduct of the country's departure from the European Union.

Anna Soubry, Heidi Allen and Sarah Wollaston said they will join eight ex-opposition Labour Party lawmakers in the new group.

In a letter to Prime Minister Theresa May, the trio accused the Conservative Party of abandoning the political centre ground, and said "the final straw for us has been this government's disastrous handling of Brexit."

With Britain's departure from the EU due on March 29 and no deal yet agreed on divorce terms, the three lawmakers accused the government of "recklessly marching the country to the cliff edge of no deal."

May said she was saddened by the decision, but said the government was "doing the right thing for our country" by implementing voters' decision to leave the EU.

The eight Labour rebels quit the party this week over its direction under left-wing party leader Jeremy Corbyn. They accuse him of mounting a weak opposition to May's plans for leaving the European Union and of failing to stamp out anti-Semitism in the party.

The defections mark the biggest shake-up in years for Britain's political parties. There have long been signs that voters' 2016 decision to leave the EU could spark a major overhaul of British politics, because Brexit has split both the Conservatives and Labour down the middle into feuding pro-Brexit and pro-EU wings.

The breakaway lawmakers hope to gain members from among disgruntled pro-Europeans in both the Labour and Conservative parties, with a view to forging a new force in the centre of British politics.