Owen Smith says he would block Article 50 if he became Labour leader

Labour leadership candidate Owen Smith has made the bold promise to block Article 50 being triggered until Theresa May agrees to wait until the 2020 general election or alternatively call a second referendum.

Smith, who has repeatedly described himself as passionately pro-EU, says Labour under his leadership would block any attempt to officially withdraw Britain from the EU by voting against it in parliament.

He launched another attack on current Labour leader Jeremy Corbyn for calling on the government to invoke Article 50 as soon as possible. Nearly two-thirds of Labour voters voted for Britain to remain in the 28-nation bloc in the June referendum.

"Under my leadership, Labour won't give the Tories a blank cheque," Smith said in a press release sent to Business Insider.

"We will vote in Parliament to block any attempt to invoke Article 50 until Theresa May commits to a second referendum or a general election on whatever EU exit deal emerges at the end of the process. I hope Jeremy [Corbyn] will support me in such a move."

He added:

"Jeremy Corbyn's decision to call for Article 50 to be invoked immediately after the referendum result was deeply irresponsible and, if he had been listened to, would have damaged Britain's interests.

" The British people were lied to by the Leave campaign - they deserve to have a say on whatever exit deal the Tories strike with the EU. Theresa May says that 'Brexit means Brexit' - but nobody knows what Brexit looks like. It could involve trashing workers' rights and environmental protections, opening our NHS up to foreign competition, making it harder for us to trade with our neighbours and damaging our economy.

"I'm a passionate pro-European, and I will fight tooth and nail to keep us in the EU."

This pledge is clearly an attempt by Smith to appeal to Labour voters who mostly support Britain staying in the EU. Corbyn's critics accuse of him failing to campaign enthusiastically enough for Britain to stay in the 28-nation bloc in the lead-up to the June 23 referendum.

However, Smith's suggestion that there should be a second referendum on Britain's EU membership, in particular, is not likely to be popular with the general public. Nearly two-thirds (58%) of Brits said they didn't support a second referendum when surveyed by YouGov in late June - including 29% of people who voted Remain.

May has said that she would not invoke Article 50 - the official process of Britain withdrawing from the EU - until early next year the very earliest.