Labour peer Lord Andrew Adonis has claimed that Brexit is a "far-right project".
The remain supporter's comments came in the wake of the news that Labour-affiliated trade unions have agreed to back a second referendum if a fresh deal is negotiated under the next Prime Minister.
And if the country is headed for a no-deal Brexit, union chiefs decided unanimously that Labour should campaign for a public vote, throwing their support behind an option to remain in the EU.
Explaining the stance to talkRADIO's Julia Hartley-Brewer, Lord Adonis said: "Jeremy's [Corbyn] views on Brexit is in flux is my best description of it.
"He clearly was historically a leaver, but he understands that Brexit has become a far-right project."
Lord Adonis, who has been a regular at People's Vote campaign rallies, warned that Brexit, both with a deal or without, would be an "extreme policy".
"What has become clearer and clearer is that there wasn't a credible leave proposition on the table.
"The big problem we've got at the moment is, is there agreement on what leave means?".
Addressing leave-voting Hartley-Brewer, Lord Adonis added: "You would do a very moderate and sensible Brexit.
"The people who are actually in charge of it, that's not what they want so it would become an extreme policy."
His comments have already sparked a backlash among Brexit supporters.
Twitter user Dawn Westcott wrote: "A far-right project?" What? How many more insults do ordinary British leave voters - across the political, racial and social spectrums - have to take from Labour spokespeople? What's Labour trying to achieve?."