Jeremy Corbyn was told to “grow up” and “get off the fence” by the SNP’s Westminster leader during a Commons clash over a second Brexit referendum.
Ian Blackford made the angry comments when one Labour frontbencher, thought to be shadow international trade secretary Barry Gardiner, blew him a kiss.
The row came as tensions rose during the Commons debate on Theresa May’s Brexit deal on Tuesday afternoon.
Blackford, whose party is Labour’s main rival in Scotland, issued a plea to his “many friends” on the opposition benches to immediately back a fresh public vote on leaving the EU.
He said: “I am appealing to the Labour party, for goodness sake, get off the fence.”
Labour has not ruled out backing a so-called People’s Vote once, as is widely anticipated, May’s withdrawal agreement is voted down.
But Blackford, who claims the PM’s Brexit deal will damage Scotland’s economy, said young Remainers who voted Labour in 2017 “would never forgive” Corbyn if he failed to get behind a fresh poll.
And he appeared to lose his temper after Gardiner’s alleged intervention.
“You can blow a kiss but what you’re doing is blowing a raspberry to the people of the UK, that’s the reality,” said Blackford.
“It really is about time, if you’re serious about politics, if you’re serious about responsibility, then grow up. Grow up and accept responsibility and don’t dodge this.”
Corbyn has said he will table a vote of no-confidence in the government “soon” but “at a time of our choosing” and that Labour remains committed to trying to trigger a general election.
His allies stress the party is weighing up when it is most likely to win such a vote, but reports have emerged it could be as soon as Wednesday.
Corbyn has also come under increasing pressure from his own side to support a second Brexit vote.
Labour shadow ministers Clive Lewis and Marsha de Cordova on Monday night called for Corbyn to back a “remain and reform” agenda.
The SNP wants the government to immediately request an extension to Article 50 and call a second referendum.
The prime minister has until Monday to return to parliament to set out an alternative plan should her deal fall.
A push for a Norway-style soft Brexit, led by former Tory minister Nick Boles, is also underway.
It is unclear which plan, if any, Labour will throw its weight behind, but party policy agreed at its conference last year states that if Corbyn fails to secure a general election “all options” are on the table.