Media playback is unsupported on your device Media caption Key Scottish Labour figures from the past two decades try to explain what went wrong

Following Labour's heavy defeat in Scotland at the general election, BBC Scotland Investigates has been speaking to former leaders, politicians and activists to examine how the party that was born in Scotland and helped shape the country came to have only one MP north of the border.

The seeds of May's catastrophic defeat may have been sown a way long back in the complacency of Labour's dominance in local government, its move away from its roots or its past political decisions.

But in 1997 Labour could not have been riding higher across Scotland and the rest of the UK.

Tony Blair's landslide victory led to a referendum on Scottish devolution and the setting up of the Scottish Parliament.

Could Scottish Labour's current problems be down to one of its greatest achievements north of the border?

The Scottish Parliament

After winning the 1997 referendum on devolution, the next task was choosing the members who would stand for election to populate Holyrood and steer the new devolved parliament.

Some claim the process was not impartial, with the party reaching for a top-down process, with Westminster, not Scottish Labour, taking a lead.

IAN DAVIDSON (Glasgow MP 1992 until 2015)

"Behind it all was Donald Dewar who was a tremendous intellectual and social snob.

"I mean Donald had a very clear view about what he wanted to have in the Scottish Parliament and he basically wanted Liberals and Labour, sort of like Glasgow University debaters and lawyers, as it were, running the whole establishment and he wanted people to come in there that were going to go along with that."

SUSAN DEACON (Labour MSP 1999 to 2007)

"It was supposed to be about the great and the good selecting the brightest and the best but what it actually did was deny the chance for a whole lot of very talented and accomplished people, including a number of sitting MPs, from actually even putting themselves forward for selection.

"That first Scottish parliamentary Labour group didn't have within it some real talents that could have been there. And I think we paid the price for that."

The death of Donald Dewar

Image caption Scotland's first First Minister Donald Dewar died the year after he took office

DAVID WHITTON (Special advisor to Donald Dewar and Labour MSP from 2007 to 2011)

"I think it was cataclysmic. The parliament had only been going for just over a year.

"The fact that Donald was not there to lead it through its first four years did untold damage to the parliament and did untold damage because the last thing we needed was a leadership vacuum at that point in time."

BRIAN WILSON (Cunninghame North MP 1987 to 2005)

"That there was no succession planning for leadership. It was a great tragedy that Donald died, but things just went from bad to worse thereafter."

Infighting and turf war with Westminster

HELEN LIDDELL (Labour MP 1994 to 2005)

"Frankly Scottish Labour could start a fight in an empty house. "

HENRY MCLEISH (who succeeded Donald Dewar as Scottish Labour leader and first minister in 2000)

"Personal care free at the point of need seems like a great step forward. But the worry at Westminster was the English may want it as well. How horrific.

"So you would have spats with the ministers, you would have some fairly hectic, intense and language exchanging sessions with them.

"People felt that, you know, it was a kind of second division parliament, and that got us off to a bad start.

"And to be honest with you, that hasn't wholly disappeared in the last 16 years."

JACK MCCONNELL (Scottish Labour leader and first minister from 2001 to 2007)

"In Scotland local government had been Labour's great powerbase through the opposition years and the creation of the Scottish Parliament, to some extent, eclipsed local government.

"And at the other end I think the Westminster MPs found it really hard to cope with the fact that suddenly there was this bunch of new MSPs who were getting more publicity in the local papers, who had more day-to-day responsibility than they had, and they found - they were defensive I think, over a long period of time."

IAN DAVIDSON (Labour MP)

"I think it's fair to say that Jack and Henry's periods were less than total successes, and I think I can understand why they would want to blame somebody else for that."

"They weren't forceful enough. They should have been doing far more for working people and their families. Simply to say a "bad boy at Westminster blocked them" all the time, isn't really good enough. I can understand why they say it, but it's not true."

Obsessed with the SNP

SUSAN DEACON (Labour Scottish government minister)

"Week on week, discussions about policy and so on were driven, not by kind of long-term aims.

"I'm thinking here, within the parliamentary group for instance - but rather about how you'd win the vote that week, what the headline would be, how we'd be seen to be getting one over on the Nats, for example, that was typically the exchange.

"And I know that many of my erstwhile colleagues will despise me for saying that, but I'm sorry, that's what it felt like to me, and that's what I disliked, and I firmly believe it's what an awful lot of the Scottish public disliked too."

The Iraq War

Of all the events said to have contributed to the fall of Labour in Scotland, and which caused damage to Labour nationally, one looms large.

Labour Prime Minister Tony Blair's decision in 2003 to lead the UK to war in Iraq.

LORD FALCONER (close friend and confidant of Tony Blair)

"I think the Iraq war damaged Labour everywhere, and I think that the Iraq war is perceived to be a mistake.

"That damaged Labour right throughout Scotland and England, but I'm not sure that it necessarily damaged Labour more in Scotland than it did in England.

"In 2005 and 2010, after the Iraq war, there were elections in which Labour were returned, once with Tony Blair in 2005 and then in 2010 in Scotland, although Labour was not returned as a national government, as I said before, it did better.

"So, yes Iraq was damaging, the question was it more damaging in Scotland than it was elsewhere, I'm not sure that it was."

Election defeat in 2007

By 2007, Labour's grip on power was slipping and the SNP became the biggest party by one seat and formed a minority government.

Labour had been the incumbent party of government in Holyrood since 1999 and at Westminster since 1997.

But now it had been eclipsed as the main party of power in Scotland for the first time in decades.

For a party unused to defeat, the recriminations started.

JACK MCCONNELL (the defeated Scottish Labour leader in 2007)

"I think there was initially defensiveness that was then added to anger after the SNP won in 2007.

"And I have to say defensive anger is not a good starting point for a political party that's trying to rebuild its levels of support.

"But that was what was driving much of Labour decision-making and tone from 2007 onwards. That there was this anger that the voters had done the wrong thing, how dare they?"

IAIN GRAY (took over the Scottish Labour leadership from Wendy Alexander in 2008)

"I think if you do any kind of job like that the dangerous thing, but the thing which nobody can avoid, is you look back and think about things that you could've done differently.

"My view of the core of our problem, this is not the only problem but I think it's at the heart of it, is the inability of the party to really come to terms with the new political context created by devolution.

"I think I maybe half understood that when I was a leader. I understand that much better now."

The election rout of 2011

IAIN GRAY (the defeated Scottish Labour leader in 2011)

"The difference between what happened to us in 2011 and what had happened four years before, was largely about a very successful SNP campaign.

"My point is not that that wasn't a bad result - it was a terrible result.

"My point is we should've seen it coming because the roots of it actually lay back in previous elections."

JOHANN LAMONT (became Scottish Labour leader in 2011)

"I think when I took over in 2011 what I wanted was for us again to be credible politically. We described it at the time as being intensive care. We'd gone through a really, really bad election. You know, this was not a job that anybody was rushing towards in order to get plaudits.

"I wanted people to look again at the Labour Party and say: 'This is an organisation that has a purpose'."

The referendum campaign

Was the referendum the cause of Scottish Labour's problems or did it just expose them?

The Better Together Campaign, which included Labour, the Tories and the Lib Dems, was supposed to show a united, pro-unionist front against independence.

However, it meant Labour being yoked to a party that had very different notions of society and what Scottishness should be.

JOHANN LAMONT (Scottish Labour leader during the referendum campaign)

"I took a view that we should be part of Better Together but I also recognise that there were people in our own party who are less comfortable with that.

"And, of course, we were having this kind of argument put back to us by the SNP, while they themselves were making that common cause, that somehow that we were doing the wrong thing by working with people in Better Together."

HENRY MCLEISH

"I believe that the Better Together campaign was created in London, and was delivered to Scotland to be implemented by the Labour Party.

"Speaking to many, many Labour Party people, they were totally dismayed by the fact that we could have a platform with the Conservatives because we have no platform with the Conservatives on anything else.

"It gave the SNP a field day and in the referendum what we found was it was the SNP and their voice of Scotland against the rest."

JACK MCCONNELL

"The whole campaign design was wrong. There should have been an independent, non-party campaign for a No vote that the three political parties then each supported in their own way with their own supporters.

"This idea that you bring the grandees of the three Westminster parties together to come and tell Scotland what to do - it's a daft idea, it's always going to be problematic but nobody would listen, and organise the campaign in a different way.

"It is an example of what was wrong with the thinking - the idea that you can dictate to Scotland how it thinks instead of actually listening and engaging with people who are active in Scotland and have got some experience of the situation."

IAIN GRAY

"I said to a number of colleagues there that we have to think about the possibility that even if we win the referendum and Scotland remains part of the United Kingdom that what will follow from that will change the next election, and that next election will be 2015 - that election will be about something different, that it will be about Scottish identity and the constitution.

"And that for the first time in many Westminster elections the SNP will be able to find a strong relevance, and if that happens then you - Labour MPs - will find yourselves competing against the SNP in the way we had to do in 2011.

"And my colleagues said: "That can't happen." I could not convince them that the referendum would change the context. So what I'm saying to you is that that's not a tension. It was a failure to really understand how Scottish politics was changing."

BBC Scotland Investigates: The Fall of Labour is on BBC One Scotland at 21:00 on Monday 22 June.