A constantly growing online petition pressing for a second referendum on the UK’s decision to quit the EU passed three million signatures on Sunday, all garnered in just 48 hours, signalling a major backlash against the shock Brexit vote.

By this morning, as many as 3,048,000 people had signed the petition on the official UK Parliament website. The figure takes it well over the 100,000-signature threshold required to trigger a debate in the House of Commons.

Ben Howlett, a Conservative MP, confirmed on Twitter that the petition will be discussed on Tuesday by the House of Commons Petitions Select Committee.

With signatures to the petition constantly rising, Labour MP David Lammy appealed to fellow MPs to ignore the result of the referendum on Friday which, he said, was only advisory. On Twitter, he wrote: “We can stop this madness and bring this nightmare to an end through a vote in Parliament. Our sovereign Parliament needs to now vote on whether we should exit the EU.

“The referendum was an advisory, non-binding referendum. The Leave campaign’s platform has already unravelled and some people wish they hadn’t voted to Leave.

“Parliament now needs to decide whether we should go forward with Brexit, and there should be a vote in Parliament next week. Let us not destroy our economy on the basis of lies and the hubris of Boris Johnson.”

The development came as some voters who had backed the “Leave” campaign took to Twitter to register their regret — adopting the #Regrexit hashtag. Meanwhile, German Chancellor Angela Merkel has called on for clear-headed negotiations with “close partner” Britain over its departure from the European Union. Foreign ministers of the EU’s six founding members had earlier said Britain should leave the bloc as soon as possible after Britons voted on Thursday to quit the 28-member bloc.

However, Merkel struck a more conciliatory tone. “The negotiations must take place in a businesslike, good climate,” Merkel said after a meeting of her conservative party in Hermannswerder, outside Potsdam, to the west of Berlin.