London (dpa) - More than 2.1 million people had signed an online petition by Saturday urging the government to hold a second referendum on Britain's membership of the European Union.
The petition to parliament said the government should "implement a rule that if the remain or leave vote is less than 60 per cent, based a turnout less than 75 per cent, there should be another referendum."
A majority of 52 per cent voted to leave, with a turnout of 72 per cent of the 46.5 million eligible voters.
Parliament is obliged to "consider for a debate" all petitions attracting more than 100,000 signatures.
Leading campaigners in the debate ahead of Thursday's referendum, including Prime Minister David Cameron - who resigned on Friday, said a second referendum would not be possible.
Labour lawmaker David Lammy on Saturday called on parliament to "stop this madness" and vote against the referendum decision to leave the EU.
"Wake up. We do not have to do this. We can stop this madness through a vote in Parliament," he said in a statement posted on Twitter.
"The Leave campaign's platform has already unravelled and some people wish they hadn't voted to Leave," Lammy wrote, calling for a vote in parliament next week.
Meanwhile, more than 148,000 people signed another petition urging London Mayor Sadiq Khan to declare the city independent from Britain and join the European Union.
"London is an international city, and we want to remain at the heart of Europe," said the petition on change.org, initiated by London-based journalist James O'Malley.
Voting in the referendum produced huge regional differences, with most areas in central and northern England returning large majorities for Leave, while London and Scotland voted strongly for Remain.