Support had soared to some 3.1 million online signatures on Sunday for a petition urging the government to call a second referendum on Britain's membership in the EU, as crises deepened inside the country's two major political parties.

The petition to parliament said the government should "implement a rule that if the remain or leave vote is less than 60 percent, based [on] a turnout [of] less than 75 percent, there should be another referendum." The "leave" camp won the support of 51.9 percent of voters, against 48.1 percent in favor of remaining in the EU. Turnout for Thursday's referendum was 72.2 percent.

Parliament is obliged to "consider for a debate" all petitions attracting more than 100,000 signatures. Leading campaigners in the debate ahead of Thursdaytarget="_blank"'>