LONDON — Three pro-European lawmakers have quit Britain’s governing Conservatives to join a newly formed centrist group of independent legislators opposed to the government’s conduct of Brexit. Anna Soubry, Heidi Allen and Sarah Wollaston announced Wednesday they will join eight ex-Labour Party lawmakers in the new group. The Labour rebels have quit the party over its direction under left-wing party leader Jeremy Corbyn. They accuse him of mounting a weak opposition to Prime Minister Theresa May’s plans for leaving the European Union and of failing to stamp out anti-Semitism in the party. 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 center of British politics.