No one who saw the scrum of photographers surrounding the Tories' defeated Eastleigh candidate Maria Hutchings, could have been in any doubt about how significant a catastrophe Thursday's by-election defeat  was for David Cameron. In assessing the significance and cause of the Conservatives' demise it's worth reminding ourselves of the lessons that emerge from this election and what it means for One Nation Labour.
The Eastleigh by-election was a tough fight for the dedicated Labour activists who worked so hard over the past three weeks for John O'Farrell. Any by-election in which you start in third is a tough ask, particularly when it's your 258th target seat. This was a very different seat from Corby, where we captured a key marginal from the Conservatives. John O'Farrell fought the odds in an excellent campaign and his result bears comparison with by-elections past. I want to thank everybody who made the trip to deepest Hampshire to help him. It says much about the enthusiasm for John's candidacy and Ed Miliband's One Nation message  that people came from across Britain (and particularly the south east) to support the campaign.
The real story of yesterday's result, however, is the failure of David Cameron's Conservatives. The conditions could not have been more favourable for them to beat the Lib Dems - this was their 16th most winnable Liberal Democrat seat. The by-election was triggered by Chris Huhne standing down in disgrace after pleading guilty to a criminal offence. Coming third behind the Liberal Democrats and UKIP was clearly a disaster for the Conservatives and their hopes at the next general election in 2015.
This by-election was a test of Cameron's judgement and on that count he failed. It will terrify him that, after making so many concessions to those on the right of his party by offering an EU referendum, a campaign focused on immigration and a candidate who - horribly exposed under the scrutiny of a by-election - wanted to leave the EU and opposed same sex marriage, he was still beaten into third place by UKIP. In the battle on the ground, the small band of Conservative foot soldiers appeared out of touch with voters on issues like living standards and fairness.
However, whilst our result stands favourable comparison with many by-elections of the past in seats where parties have started as long shots, this result shows that we need to redouble our efforts to reach out to every part of the country, including areas where Labour hasn't traditionally been strong.
Labour listened to voters on the doorstep, and we will learn from what they told us. All mainstream political parties need to take seriously the concerns people have about the country, whether it is the cost of living, fairness or immigration. Under Ed Miliband's leadership, Labour is determined to meet those concerns.
But we should be in no doubt - this was a disaster for David Cameron. If he can't win a seat like Eastleigh, the Tories will be very worried that he can't win the other seats they need at the next general election in 2015.
Toby Perkins MP was Labour’s campaign manager in Eastleigh