Shadow business secretary Chuka Umunna has questioned why politics had to be a blood sport, saying: "I don't think George Osborne is the devil."
Addressing a fringe event at the Labour Party conference, he said many people in "communities that have supported us" for years were unwilling to back the Labour-backed Better Together campaign.
He said the "wrong lesson" to learn would be to focus solely on current or previous core Labour supporters.
This was in sharp contrast to remarks by the leader of the Unite union, Len McCluskey, who told delegates Labour had had a "near-death experience" in Scotland.
"Let the referendum be the tombstone on 20 years of our party's indifference to the interests of the working class," he said.
But the shadow business secretary, speaking at an event organised by The Times, argued: "We are only going to get into office if we build a big tent."
He pointed out that in 1997, when Labour gained a landside majority, it won 56 seats in southern England outside London, but in 2010 this had dwindled to just 10.
"I think never before have we had to get out of our comfort zone more than now," he said.
The remarks from both men highlight again how dominant a theme the Scottish independence referendum and its implications has become at this conference.
But Mr Umunna had other topics he wanted to address. He acknowledged the need to look again at the free movement of labour in the European Union - a core principle for Brussels - saying it was being used "in a way that wasn't intended."
"People have legitimate concerns about how people are counted in and out," he said, adding that when he worked alongside his predecessor as MP for Streatham in south London, Keith Hill, "I was shocked at how chaotic the system was."
"We also have to acknowledge that when the EU was created there was far fewer members and less diversity in its economies," he pointed out, a reference to the poorer countries from eastern and central Europe that have joined the European Union in the last decade.
Pushed by interviewer Philip Collins as to why polls suggested Labour was struggling to convince many voters it could be trusted to run the economy again, Mr Umunna admitted "undoubtedly there were things that happened under our watch... We are having to deal with that legacy."
"One thing we could have done earlier during our time in office was talked more about the cuts and consolidation," he said, adding that if Labour did win next year's general election "we are going to deliver social democracy in a cold climate". But he added that "in 1997 we froze spending for two years but we massively improved Britain".
He said that between now and polling day "we are going to have absolutely everything thrown at us. It is going to be nasty. It is going to be personal." But he pleaded for politics to be "less tribal".
"The way that we do politics is pretty ridiculous when people are less tribal. I don't think George Osborne is the devil. Why does politics have to be a blood sport?"