A former Labour MP who led the party's campaign to stay in the European Union says Jeremy Corbyn's Brexit approach could see the party "steamrollered" in a general election.
Alan Johnson, who was MP for Hull West and Hessle for 20 years and served as Home Secretary and Health Secretary, criticised Mr Corbyn after he refused to clarify whether he would back Remain or Leave in a Brexit referendum he would call as prime minister.
The Labour leader did not rule out remaining neutral in a referendum giving the public the option between a "credible" new exit deal he would negotiate and staying in the EU.
Senior shadow cabinet colleagues including John McDonnell, Tom Watson and Emily Thornberry have been vocal in saying they would back Remain, regardless of any deal secured by Labour.
And Welsh Labour further exposed the rift by saying they would campaign to stay in the EU, shortly after Mr Corbyn outlined his plans to offer a "sensible" Brexit option.
Mr Johnson, who led the Labour In campaign during the referendum, told BBC Radio 4's World at One that the Labour leader's approach could be approved at party conference because it's "a pragmatic way to try to avoid the extremes".
He added: "My fear is if you go into the next election without Europe being sorted it's going to be the most toxic, horrible, nasty and unpredictable election that probably we've ever had in this country.
"And the people in the middle that are trying to suggest 'let's try and get a deal here somewhere' are going to get mowed down. There's an awful lot wrong with it.
"My main fear is Labour will be steamrollered by the two extremes if they've got this neither one thing or the other thing in the middle."
In interviews yesterday, Mr Corbyn would not make clear which option he would prefer when asked repeatedly.
"My job as prime minister would be to deliver that option that's chosen by the British people," he said.
"I will credibly present the options and say 'this is the option, you can Remain, possibly with some reforms to the European Union, or you can Leave, but you will be leaving on these terms which would protect jobs and living standards and trade'."
Pressed if he would remain neutral in the campaign, Mr Corbyn said: "As prime minister I'm offering the people a choice - the only party that's doing so."
The Liberal Democrats have hardened their pro-Remain position, with leader Jo Swinson now vowing to revoke Article 50 immediately if her party won a general election.
Prime Minister Boris Johnson has taken the hardline approach of vowing to force Brexit through by the October 31 deadline, regardless of whether a deal is in place or not.
Mr Corbyn's signalling that he could take a neutral position in a referendum campaign came days ahead of his party conference, where he is expected to come under pressure to take a stronger Remain stance.
During the interview, Mr Corbyn said he would win the support of his unequivocally Remain-backing colleagues going forward.
"I've shared these views with all of my colleagues in the party and I'm very confident they will come with me on this journey to make sure that the people of this country make the final decision," he said.
Mr Corbyn wants to negotiate a deal with Brussels that would include a new customs union with the EU, a close single market relationship and guarantees of workers' rights and environmental protections.