Campaigners for a second referendum to stop Brexit have just a few weeks left in which to persuade Members of Parliament to back a second referendum.

MPs backing the campaign admit that they don't currently majority support in Parliament for another vote.

There are growing disagreements in the campaign about what to do next.

The campaign is now throwing its support behind two Brexit amendments which could just leave the door open for a People's Vote.

LONDON — Anti-Brexit campaigners believe they might have just days to persuade the UK Parliament to open the door to a second Brexit referendum or see their hopes of calling a so-called People's Vote start to fade away.

On Thursday MPs representing the People's Vote campaign said they would not next week bring forward a House of Commons vote on whether to hold a referendum before Brexit, citing the lack of support from Labour Party leader Jeremy Corbyn.

"We could have the numbers if we had the unequivocal support of Jeremy Corbyn," Conservative MP and supporter of the People's Vote campaign Sarah Wollaston a told journalists on Thursday morning.

However, with the chances of securing immediate parliamentary support for a second vote currently looking slim, the campaign is instead throwing its support behind a series of Brexit amendments which could hand MPs the power to both delay the UK's exit from the European Union and decide what the government should do next.

Business Insider has spoken to several campaign figures who have revealed growing disagreements and doubts about this decision to delay a clear vote on a second referendum, as well as their broader strategy to secure a People's Vote.

Shooting down the alternatives

Having decided not to push for a immediate parliamentary vote on a referendum, the People's Vote campaign will next week back a new Brexit amendment, brought forward by former Conservative minister Dominic Grieve, which could allow MPs to hold a series of so-called indicative votes on what to do next.

Campaign strategists believe that this process will help their tactic of demonstrating that a second referendum is the only way left to settle the Brexit question.

"The plan is to knock every option down until a People's Vote is left. And give enough time for Corbyn to move," a senior figure in the campaign for a new referendum told BI this week.

The plan is to knock every option down until a People's Vote is left.

It is for this reason that so much recent People's Vote material has targeted forms of "soft Brexit," like the Labour Party's policy of a full customs union, and the so-called Norway Plus model of staying in the single market and customs union.

They believe this strategy will eventually leave MPs with a binary choice: no-deal or a referendum.

However, not everyone in the People's Vote movement supports this approach.

A senior source in one of the pro-People's Vote opposition parties described it to Business Insider as "f***ing mad."

They added: "The thing is, we are now angling in the exact same way as Downing Street. For them, it's May's deal or no deal. For us, it's referendum or no deal."

The strategy has also caused open criticism and disagreement on social media between pro-referendum politicians and activists, many of whom believe that a soft Brexit should not be ruled out by the campaign as an alternative.

There is also a belief in Westminster that the Scottish Nationalist Party, Plaid Cymru and other MPs who currently support a People's Vote could ultimately back a Norway-style, soft Brexit if it became a realistic prospect.

Running out of time

The decision to abandon a Commons vote next week on holding a second referendum caused strong disagreement among MPs backing the campaign.

BuzzFeed reported this week that MPs like Chuka Umunna and Wollaston herself had wanted to table a motion to the government's amendment on Tuesday but senior People's Vote figures urged them to be more patient.

A Labour MP who supports the campaign said that while another referendum didn't yet have the support of a majority of MPs, they believed there wouldn't be many more chances for MPs to create a path to a new referendum.

"There will be other opportunities along the way but not in the hands of the House of Commons," they said, adding that future opportunities to legislate for a referendum "would be in the gift of the government."

"We are running out of time," they added.

Such was the disagreement over the decision to put off the vote that some MPs on the campaign "needed to be strong-armed into agreeing" to the move at a meeting on Tuesday, a source familiar with those discussions told BI.

A source who works for the People's Vote campaign said this description was "over the top."

This internal disagreement culminated in Wollaston, Umunna and other MPs who support the People's Vote campaign making a public statement outside Westminster on Thursday which was not sanctioned by the campaign itself.

"It is up to MPs what amendments they table and when. The priority for the People’s Vote campaign is to get majority support for the ‘take back control amendments’ before the Commons on Tuesday," a campaign spokesperson said.

READ MORE: Second Brexit referendum campaigners fear it's 'game over' unless Corbyn backs a People's Vote

There is also concern among MPs that the campaign now hinges on amendments brought forward by Grieve and Labour MP Yvette Cooper next week being passed. Both votes are expected to be close with Labour MPs from Leave-voting seats set to oppose them.

That's why the People's Vote campaign is urging supporters to lobby MPs to back the amendments, which it is calling the "take back control" amendments, in deliberate imitation of the successful campaign slogan of the pro-Brexit campaign in 2016.

Campaign supporter Guto Bebb MP said on Thursday: "None of these amendments would, in themselves, bring about a People’s Vote and all of them will gain votes from MPs who currently do not support our campaign.

"But they would give Parliament the time and space it needs, without the threat of a deadline or no deal, to make an honest assessment of different versions of Brexit."

The Corbyn conundrum

These earnest discussions about short-term strategy are taking place against a backdrop of wider debate among People's Vote insiders about what approach the campaign should take in the months ahead.

Under the stewardship of senior figures like ex-Labour communications chief Tom Baldwin, the campaign has invested time and money in opinion polls as a means of illustrating public support for its cause.

Multiple sources have expressed frustration with this approach, particularly the intense focus on polling Labour Party members and supporters.

One People's Vote campaigner told BI: "Because the campaign is full of ex-Labour spinners it is trying too hard to change the Labour Party, rather than trying to change politics."

Because the campaign is full of ex-Labour spinners it is trying too hard to change the Labour Party, rather than trying to change politics.

The focus on the Labour leadership has raised suspicions among those close to Corbyn, that the campaign is partly just a vehicle to marshal opposition to his leadership and even launch a new political party.

This has not been helped by the fact that many of the leading figures in the campaign are long-established critics of the Labour leader, from former prime minister Tony Blair, to one-time Labour leadership contender Umunna.

One source close to Corbyn told BI that they believed Ummuna, who has been one of the chief spokespeople for the campaign, was deliberately using it as a platform to forge a new party.

"There is a lot of noise that he will come out for [a new party] very soon with the pretext being that the leadership are trying to block a second referendum. I'm guessing that would be his pretext and we've been expecting that for some time."

Umunna strongly denies suggestions at that he plans to create a new party.

Despite growing differences over strategy, anti-Brexit campaigners believe that while around just 175 MPs currently support holding a new referendum, as BI reported this month, that number would rise significantly if a new vote was the only way of averting no-deal.

A senior pro-EU Conservative MP estimated that around 15 government ministers including members of Theresa May's Cabinet would resign to back a referendum if the only alternative was a no-deal Brexit.

However, the claim put forward by Wollaston and Labour MP Luciana Burger on Thursday that Corbyn's support was key to unlocking a parliamentary majority for a new referendum is questioned in Westminster.

Labour MPs from Brexit-voting seats say that an instruction from the Labour whip wouldn't be enough to persuade them to forget their strong reservations with asking constituents to vote again.

MPs are becoming less and less bothered about party discipline. As one Labour backbencher from a Leave-voting seat told BI recently, "political parties don't exist anymore... I cannot remember the last time I spoke to the whip."

Political parties don't exist anymore... I cannot remember the last time I spoke to the whip.

And while Corbyn is undoubtedly under growing pressure from a strongly pro-EU party membership, it is not a one-way street. Over a dozen shadow ministers have reportedly threatened to quit if Corbyn backs a new referendum.

A source close to the Labour leadership told BI this week: "It's clear the numbers aren't there and we're focusing on working with parliament on proposals that can carry majority support."

Despite this, the Labour leadership remains officially open to the principle of a second referendum and this week brought forward their own Brexit amendment which could allow MPs a vote on holding a second referendum.

However, with or without Corbyn's support, time is running out for those MPs who want the British public to have another say on leaving the EU. For the battle to secure that vote, next week will be decisive.