Labour's deputy leader Tom Watson has stood by Jeremy Corbyn and said it is not the time to replace his party's under-fire leader.
It follows a "hugely disappointing" defeat in the Copeland byelection and a scathing attack by David Miliband who said the Labour Party was at its lowest point in 50 years.
Watson admitted Labour needed to have a "hard look" at itself, but said another leadership campaign would further damage the party.
Speaking at the Scottish Labour Party conference in Perth on Saturday (25 February), Watson said: "Gareth Snell will be a great MP, and sending Paul Nuttall back home with his tail between his legs is exactly what he deserved.
"But I'm hugely disappointed that Gillian Troughton won't be joining him in Parliament as the MP for Copeland.
"That means that all of us with leadership roles in the Labour Party need to have a long, hard look at ourselves and what's not working.
"Seven years into a Tory government, we shouldn't be facing questions about whether we can retain the seats we already hold.
"Our job at the next election is to gain over 100 seats. Keeping what we have is supposed to be the easy bit."
Watson used Scotland as an example of the type of collapse that can happen if Labour failed to get its message right. In the 2015 general election, Labour lost 40 of the 41 seats it held in Scotland.
He added: "I've said it a lot recently. This is not the time for a leadership election. That issue was settled last year. But we have to do better. We cannot sustain this level of distance from the electorate, from our natural supporters."
The loss in Copeland was the first time a governing party had taken a seat from an opposition party in a byelection since 1983. Labour had held the seat since 1935, when the constituency was known as Whitehaven.
One leading trade union figure warned Corbyn he had to "turn things around", but the 67-year-old remained defiant in the face of calls for him to resign.
"I was elected to lead this party. I am proud to lead this party," Corbyn said. "We will continue our campaigning work on the NHS, on social care, on housing."