“If we lose Cheltenham, we’re in real trouble,” Liberal Democrat strategists told each other before the election. So when the early polling returns in Cheltenham suggested that Martin Horwood had been trounced, the Lib Dems faced the worst election result in their history: 57 seats won in 2010 became just eight in 2015. “The little party always gets smashed!” Angela Merkel told David Cameron in 2010. She was right.

The Lib Dems had long known that the election would be brutal – just not this brutal. Within a few months of the coalition being formed, the party had quietly written off several seats. Yet until the exit poll came out at 10pm on election night, senior Lib Dems, backed up by internal polling, were convinced that the party would retain upwards of 20 seats. Constituency polling by Lord Ashcroft suggested the same.

National polls were similarly deceptive. Had the polls reflected what was actually happening, the electorate might have been more receptive to warnings about the dangers of a majority Tory government. “If the polls they had shown the Conservatives ahead all the way through the campaign, the message we were pushing would have had much more traction,” asserts Paddy Ashdown, Chair of the Lib Dems’ General Election Committee.

Flawed opinion polls also allowed the Conservatives to stoke fears of the SNP allying with an unpopular Ed Miliband. The line particularly resonated in the 27 Lib Dem sears that went blue, including 14 between Cheltenham and St Ives, causing those who voted Lib Dem in 2010 to switch to the Tories.

“It was happening on the doorstep in every one of these seats across the country,” an insider says. Panicky conference calls were held between Lib Dem HQ and MPs and campaign teams across the Southwest. While the Conservatives had a simple solution – get a Tory majority to stop Labour and the SNP – the Lib Dem message was never going to be as powerful, despite their insistence they would avoid any deal with the SNP. A senior source believes that the fear of the SNP alone cost the Lib Dems a dozen seats.

National fears trumped the usual Lib Dem strength of assiduous local MPs. In strongholds like the Southwest, the Lib Dem campaign was as energetic as ever. It wasn’t enough. “Incumbency wasn't the magic wand that we all thought it would be,” Stephen Williams, ousted as MP for Bristol West, reflects. He believes that the use of social media and direct marketing in the campaign renders old-fashioned door-knocking comparatively less important. Ashdown also suggests that Tory challengers were helped by “the extraordinary financial imbalance in modern politics - they had £50 million to throw at their election campaign, I had less than £3 million.” Those organising the Lib Dem campaign on the ground report being outspent by the Conservatives like never before. They also had no money left to conduct polls during the campaign; by May 7, the Lib Dems were allocating their limited resources based on internal polls that were almost two months old.

For all the furore over the SNP, many – perhaps even most - 2010 Lib Dem voters had long been lost. Those who backed the Lib Dems as a left-wing alternative to Labour were aghast at the very formation of a Conservative-Lib Dem coalition. The initial ‘coaliscious’ phase, designed to alleviate concerns that coalition was inherently unstable, went rather too far, creating the impression that the Lib Dems had chosen to align with the Tories out of affection.

In the second half of the Parliament, partly at the behest of Clegg’s South African election strategist Ryan Coetzee, the Rose Garden marriage gave way to ostentatious ‘differentiation’: the act of publicly picking fights with the Conservatives, epitomised by Nick Clegg’s conference speech in 2013, in which he bragged about 16 Tory policies that the Lib Dems had blocked. This risked overcompensating for the warmth of the coalition’s early existence and letting the Conservatives claim all the credit for the successes of the government, as Jeremy Browne repeatedly warned. “No crystal ball was necessary, but I was speaking to myself,” he reflects.

In a sense the Lib Dem approach was the worst of both worlds. “If you spend the first half of Parliament alienating the centre-left and the second half suggesting to centre-right people that you don't really like the Conservatives very much you run the risk of alienating everybody,” believes a senior insider.

After the grand promise to transform British politics in 2010, the Lib Dems fought a deeply defensive campaign, vowing to give Labour a head and the Conservatives a heart. It seemed centrism based mostly on belief in ‘splitting-the-difference’ for its own sake: “entirely negative” and “the most ‘small c’ conservative party”, as Browne had said earlier this year. “We were not clear about what we were for,” a senior source laments, seeing 341 lost deposits – compared with none in 2010 – as evidence of a party the public thought “had nothing to say.” A campaign insider in the Southwest bemoans: “People just didn't believe we’d stopped things or delivered things.”

Yet alternative strategies might not have been any better. In the European elections a year ago, the Lib Dems fought an unabashedly positive campaign as the party of in – and did even worse. And while aligning more strongly with the Conservatives might have helped some Lib Dems in the Southwest cling on, this tactic would have risked being seen as a mere addendum to the Tories. “It would be saying that this party is now becoming centre-right,” an insider says. “It would compromise the purpose of the party: to be a liberal party.”

Among the party’s two leadership contenders, there is conflict about where the party should go next. Norman Lamb represents a continuation of the equidistance strategy, while Tim Farron, the strong favourite, is obviously far more aligned with the centre-left.

For all the disagreement over where the party goes next – and universal condemnation of how the tuition fees increase was handled five years ago – the tone of Lib Dem debate is notable for the lack of acrimony. “In the end no matter what we did it just wasn’t going to make a difference,” Williams reflects. There is a running Lib Dem joke that only a coupon election, as in 1918, would have saved the party.

But for a party that ended just 25,000 votes short of a wipeout, Lib Dems are oddly defiant. One insider describes the scale of the party’s losses as “cathartic” for MPs and the public alike; “Our stock price is so low that it offers a buying opportunity,” Vince Cable quipped in the New Statesman. Over 13,500 members – including a high proportion of the professional middle-classes who once embraced the SDP - have joined since May 7, providing an antidote to the gloom. “This is our SNP moment,” proclaims Paddy Ashdown. “People suddenly understand what we stand for - more by our defeat than when we were fighting the election.” If the Conservatives lurch to the right, it will provide the best advert for the Lib Dems’ worth. “It’s very hard to prove a negative,” an insider reflects. “Well, we can prove it now.” Conservative governments on the retreat – as in 1970-74 and 1992-97 – have provided the best conditions for the party to grow in the past.

Even so, senior Lib Dems already accept that winning 15-20 seats would be a good result at the next election. What an insider calls the party’s existential question – “How do we get into power without compromising ourselves electorally?” – may not need answering for a long time yet. As a senior figure puts it: “We should be encouraged by the fightbacks of the past but nothing is inevitable. We might fail.”