Jeremy Corbyn has mistakenly thanked Nicola Sturgeon's Scottish National Party instead of his Scottish Labour MPs during a speech intended to rally his party after a humiliating by-election defeat.
Speaking at the Scottish Labour Party Conference, the Labour leader said: "I'm delighted that Scottish Labour announced yesterday a new policy to use the powers of the Scottish Parliament to increase child benefit, which will lift thousands of Scottish children out of poverty.
"Well done Scottish Labour and well done our SNPs... MSPs for keeping that up."
And he almost repeated the mistake seconds later.
Pressure is mounting on the embattled leader following Labour's defeat by the Conservatives in the Copeland by-election on Thursday, which has prompted calls from some Labour MPs for Mr Corbyn to quit.
Labour's defeat was embarrassing because it was the first win by the Government over the Opposition in a by-election since 1982, when Labour was also split and led by an unpopular left-wing leader.
Copeland is also a seat which had been solidly Labour since it was created in 1983.
But addressing Scottish Labour supporters in Perth on Sunday, Mr Corbyn remained defiant about his position and asserted: "Now is not the time to retreat, to run away or to give up.
"If we stand together I am confident we can turn back the Tory tide and reconnect Labour with our working class voters and values, so we can win power and rebuild and transform Britain for the many, not the few."
Earlier, his deputy leader Tom Watson challenged union boss Len McCluskey and Mr Corbyn's other "cheerleaders" to be more public in their backing of the under-fire Labour leader.
He said those who helped Mr Corbyn claim victory in last year's leadership election should be supporting him in the bad times as well as the good.
"If I've got some frustrations, it's that those people that are Jeremy's cheerleaders, that made sure that he was elected for the second time last September, they should be sticking with their leader in the bad times, not just the good," Mr Watson told ITV's Peston on Sunday.
"Dave Prentis has spoken out, but I'd say to you this morning where's Len McCluskey defending his leader in their difficult time?
"It shouldn't be just down to me who represents a different tradition in the Labour party, defending our leader."
A Unite spokesman said it was Mr Watson's job to address the issues facing the party, while Mr McCluskey had been "working flat out to defend Unite members' pensions in the nuclear sector and at BMW, and to save Vauxhall jobs and plants".
Mr Watson insisted the party can win the next general election under Mr Corbyn's leadership and that it was not "a suicide approach" to stick with him "but things have to change".
"I think the country now knows that he is a conviction politician.
"I think they now want to see that he can give greater policy coherence and greater clarity when explaining what our mission is."
He said the party needed to "stop dwelling on the past" and to enter into "a damaging leadership election... we will be an irrelevance in the minds of British voters".
"Brexit is the backdrop of British political life for the next two years - it needs to be our focus," he said.
"Everything else is a distraction from that."
Wigan MP Lisa Nandy, said it was no good Mr Corbyn blaming globalisation and a rigged economy for results like Copeland.
"I think the trouble with looking at every factor apart from Labour is that it's just a severely inadequate response," she told Sky's Sophy Ridge on Sunday.
"If we really want to address what has been happening to the Labour Party for a very long time, then we as a party need to get out of our comfort zone and start confronting some of the very difficult issues that we face."
Labour's London Mayor Sadiq Khan told Sky News: "Jeremy Corbyn is the leader until he says otherwise.
"We can only serve people - repair the NHS, fix the education system, make sure we help businesses create jobs, growth and prosperity - if we win elections.
"Council elections, elections to be the mayor, by-elections and the general election. And the job of all of us is to make sure Labour gets back in to the habit of winning elections."