A new Brexit referendum could be held as soon as May 30, former Tory minister Justine Greening has said. 

The ex-education secretary has “calculated” a second EU vote would take just 22 weeks to organise if Article 50 – the timetable which dictates when the UK will leave the bloc – could be extended by four months. 

It comes as questions swirl over how parliament will break the deadlock around Theresa May’s potentially doomed Brexit plan. 

Speaking at an event organised by the People’s Vote campaign in London, Greening said: “I’ve worked out that you could plan and hold a referendum in 22 weeks.

“We could do that in 22 weeks. We could actually, after this vote on December 11, hold a referendum, potentially, on May 30 next year.

“We could, alongside that, choose to extend Article 50, I’ve suggested, by four months to July 29.”

Greening, who backs a second referendum, also set out a five-point plan as to how a re-run of the vote could be achieved. 

It would involve a referendum motion, legislation, extending the Article 50 deadline with the EU, formulating the question on the ballot paper `and “a fair campaign”. 

Voters should be allowed to choose between May’s deal, no deal and remain, Greening believes.

What could be on the ballot paper in a second EU referendum:

Which terms do you want the United Kingdom to adopt for its future relationship with the European Union? 

1. Current terms – Remaining in the EU on current terms

2. The government’s terms – Accepting the terms that have been negotiated 

3. No-deal terms – Leaving the EU on World Trade Organisation terms

There is a widespread expectation the deal May has negotiated will be voted down by MPs on December 11. The UK is due to exit the EU on March 29, 2019.

Shadow Chancellor John McDonnell also heightened the prospect of a second vote by telling the BBC it would be “inevitable” Labour would back another referendum if the party could not force the government to call a general election in the event of May’s deal being defeated. 

Greening told people at the event at London’s Southbank Centre: “MPs know that Parliament is gridlocked. That’s the reality. It’s been clear for months now. Wasted months. And it gets more surreal by the day.

“We’ve now got the prime minister actually touring the country to persuade people to back her deal, whilst simultaneously being adamant she won’t give people a say through a people’s vote. 

“If parliament can’t reach a compromise, the people should be allowed to do it themselves. In fact they must.” 

The EU and the prime minister, meanwhile, have insisted that May’s deal is final and there is no better offer. 

The PM told the Commons liaison committee on Thursday morning that extending Article 50 would mean the deal would be up for renegotiation.

She said: “What is clear is that any extension to Article 50 – anything like that, reopens the negotiations – reopens the deal. At that point, frankly, the deal can go in any direction.

“We would simply find ourselves in a period of more uncertainty, more division in this country.

“Now is the time for this country to come back together and to look at our future outside the European Union.”