The Labour Party was born out of the trade union movement in 1900 with the aim of giving a political voice to the working classes.
Gordon Brown took over as leader and PM from Tony Blair in 2007
The creation of a national government during World War I gave the party its first ministers and a taste of political power.
After the war, the decline of the Liberal Party saw Labour becoming the main opposition party, but although twice in power, Labour governments were short lived.
It was World War II that finally changed the party's fortunes.
In the coalition government that took over in 1940, the Labour leader Clement Attlee became deputy to Winston Churchill. The Beveridge Report, prepared during the war years heralded the welfare changes that would follow in peacetime.
But the scale of the Labour landslide at the 1945 election came as a shock even to the party's own supporters.
Post-war Britain saw the creation of the welfare state and the nationalisation of key industries like coal, steel and the railways. But disappointment followed; the Tories won the 1951 election, and an era of prosperity helped to keep Labour out of power for 13 years.
In the 1960s, under the leadership of Harold Wilson, a rejuvenated Labour Party clawed its way back to power.
But the new administration was bedevilled by economic problems, leading to the devaluation of the pound and in 1970, the Conservatives returned to power.
Ramsay Macdonald was the first Labour premier
By 1974 Labour was back, winning two elections in the same year, but facing new problems.
After the surprise resignation of Harold Wilson as party leader, Jim Callaghan became prime minister. He quickly found himself presiding over an economic crisis, requiring a hefty international loan and cuts in public spending.
But the final straw for many voters was the sight of the country being paralysed by union disputes during the "winter of discontent".
At the 1979 election, Labour was voted out and Margaret Thatcher moved into Downing Street. It marked the start of 18 years in opposition for Labour, and one of the bleakest periods in the party's history.
The Conservatives were to win four elections in a row.
During Labour's wilderness years, the party leadership passed first to the left-winger Michael Foot, whose manifesto for the 1983 election was later described as "the longest suicide note in history".
Mr Foot was followed by Neil Kinnock, who set about modernising the party.
But while Labour was slowly edging back towards power, Mr Kinnock was unable to steer it to the ultimate victory.
He was succeeded by John Smith, a highly respected figure in Parliament, widely seen as the prime minister in waiting. His sudden death in 1994, after a heart attack, was a shattering blow for the party.
Harold Wilson was prime minister in the 1960s and 1970s
In the contest that followed, Tony Blair was elected leader and the process of modernisation begun by Mr Kinnock continued with a vengeance.
The architects of "New Labour" were pitted against the forces of tradition, with their attachment to socialism - regarded by the leadership as an electoral liability.
In a symbolic break with the past, the Clause 4 commitment to nationalisation was torn up.
Re-positioned as a party of the centre-left, Labour approached the 1997 election at a time when the Conservative government appeared to be running out of ideas. Individual Tory MPs were also tainted by allegations of "sleaze".
The result was a landslide victory that made Tony Blair Prime Minister.
Labour had committed itself to modernise Britain and build a fairer society. Mr Blair made it clear the unions would be treated fairly but without any favours, and Labour would welcome business as a partner.
In government, the party clearly intended to hold the middle ground.
Neil Kinnock set about modernising the Labour Party
A second term followed, and in 2005, so did a third, but after a campaign overshadowed by public anger over the Iraq War, Labour emerged with a greatly reduced majority.
A tough couple of years followed, with by-election defeats, cash-for honours allegations and rows over controversial policies like ID cards and 90-day detention for terror suspects.
Labour also faced a fresh challenge from a rejuvenated Conservative Party under new leader David Cameron.
In September 2006, Mr Blair announced he would stand down within the year. When he did so the following June his Chancellor Gordon Brown took over without a contest, after his only rival - left-winger John McDonnell - failed to get enough nominations.
After deciding against calling a snap general election in autumn 2007, when the party was enjoying the so-called "Brown bounce" in the polls, May 2008 saw Labour's worst local election result in 40 years.
Then, after years of economic boom, the credit crunch hit, forcing Mr Brown to bail out the banking sector and ratchet up Britain's deficit.
He positioned himself as "a serious man for serious times" whose government had "led the world in saving the banking system".
Tony Blair became Labour leader in 1994 after John Smith's death
And in a move that surprised many, Mr Brown ended a long-running feud with Peter Mandelson - one of the architects of New Labour - and brought him back into the cabinet from his post as EU trade commissioner.
But as one returned, others left - ministers James Purnell, Charles Clarke, Geoff Hoon and Patricia Hewitt all came out to say Brown was bad for Labour's chances of extending their record period in office to a fourth term.
The MPs' expenses row in 2009 hit all the major parties, but the Conservatives did their best to paint it as the product of a system allowed to fester by Labour for more than a decade.
Labour may fear the scandal has simply fuelled a desire for change - of any kind - at the coming election.
If they are looking for inspiration from history, they need look no further than their most recent election defeat - 1992 - when John Major showed it was possible for an incumbent party to win a fourth term despite the country being hit by recession.