Some people are saying we need a long period of reflection to understand what went wrong in the general election and how we got our worst result in terms of seats since 1935. We need everyone in the party to understand why we lost, and act on the lessons when they cast their votes for a new leader and deputy. But it’s not rocket science. It’s not complicated. It’s blindingly obvious why we lost and any ordinary voter would be able to tell us.

But accepting it means people must admit that they have been indulging in a dangerous delusion for four years – or, in some cases, known exactly what the consequences would be but propped it up for the dubious CV advantage of a shadow ministerial job, or mouthed the required platitudes, or simply shut up in order to avoid confrontation. I’d ask the people in the latter two categories what the point is in their being in politics, as opposed to climbing the greasy pole in an accountancy firm or any other career, if you don’t say what you believe in? Actually, that’s unfair on accountants who have a professional duty to call out dodgy accounting practices, rather than going along with them for a quiet life.

The general election results were a tragedy for the Labour Party and the people we exist to serve. They have opened the door to a hard-right Tory majority and put us even further away from power than in 1983. Having already lost Scotland, we have now lost other century-old pillars of our parliamentary coalition in the former coalfields and industrial areas of the North East, North West, Yorkshire and the Midlands.

This result was entirely self-inflicted and inevitable when members elected Jeremy Corbyn twice. They allowed him and his supporters to destroy Labour’s reputation with voters, our internal unity and harmony and – by bringing antisemitism into the heart of Labour – our moral standing as an anti-racist party. Labour can’t win with politics, rhetoric and leaders from the hard left. We knew that after 1983 – why did we have to run the same experiment twice?

We took what was already a catastrophic situation in 2015, when voters were afraid of what Ed Miliband meant in terms of weak leadership and lack of credibility on economic policy. We then doubled down on it – sending ordinary voters, many of them the working-class people our party was set up to represent, into the arms of Boris Johnson because they were frankly terrified of a Labour government.

Terrified that Jeremy Corbyn was at best a weak leader who couldn’t come to a clear position on Brexit, the most important decision facing the country. And at worst, he was a threat to national security given his lifetime of support for extremist regimes like Venezuela and Cuba, empathy with terrorist groups like Hamas, Hezbollah and the IRA, hostility to nuclear deterrence and the armed forces, and appeasement of hostile regimes like Russia (his polling numbers took their biggest hit during the Skripal poisoning case, when he wouldn’t condemn Russia for attempted murder on our soil).

Terrified at the economic consequences of our proposed spending splurge – for which Corbyn couldn’t make the sums add up during his car crash interview with Andrew Neil.

Terrified at letting a Heinz 57 varieties of Stalinists, Trotskyists and ultra-left cranks from LOTO (the leader’s office) hold security-sensitive jobs in 10 Downing Street.

Terrified of the obsessive focus on nationalisation of an array of industries in our manifesto and what it would do to inward investment.

Terrified of the chaos that would ensue if a government tried to enact a manifesto that was a wish list of hundreds of individually attractive ideas, with no prioritisation about what was affordable or achievable.

Terrified about the bullying and aggression inside the party from the hard left and what it would develop into if given state power.

Terrified about ministerial decisions being taken by people who are obviously incompetent, second-raters.

If they were Jews or anyone that cared about Jews, terrified about antisemitism being brought into the heart of government decision making. That fear cost us five marginal seats.

Terrified by rhetoric about “transformational government” and activists whose understanding of socialism is about literally abolishing the economic system – people want their lives improved, not turned upside down.

Terrified by rallies full of people who look nothing like the median voter wildly applauding ranters and ravers.

The problem with having a counter-cultural leader and activists is that, if you stand in opposition to the mainstream culture of a country, you can’t possibly win a democratic election. The problem with having a leader and activists who proudly come from the furthest left part of the political spectrum is that voters are distributed on a bell curve – with most being in the middle.

This election was most like George McGovern vs Richard Nixon in 1972. McGovern, like Corbyn, was wildly popular on campuses and with college-educated young people. He only won Massachusetts and DC because his radicalism terrified blue-collar Democrats, including unionised workers, and pushed them into the arms of Nixon.

In 2015, I wrote: “A crucial chunk of voters whose support we need to win in the future read the Sun or the Mail not the Guardian, and are not poor or young or from a minority background. In the suburbs and middle-sized towns that make up most of the swing seats between Labour and the Tories this is even more the case.

“We had nothing to offer to these ordinary people, who had happily voted Labour in 1997, 2001 and 2005, to persuade them to take the risk of changing government. We were unable to explain why we should be any more trusted with the economy than in 2010. We failed to understand that most ordinary swing voters if in work and in good health have either not been affected by austerity or actively welcomed a bit of belt-tightening by the public sector.

“Any good Marxist will tell you that the primary determinant of electoral behaviour is personal, material self interest. We seemed to ignore that and assume there would be enough altruistic people in the middle to top-up the base of poorer voters our policies would have benefitted. There aren’t.”

All of this remains true but instead of acting on it, we doubled-down. And as well as being our worst seat total since 1935, this was easily our worst ratio of seats per vote, as we still piled up majorities in inner city areas whilst losing scores of marginals narrowly. The poor targeting – both political and organisational – reflects the utter amateurism of our head office operation.

Everyone with experience of organising elections and targeting was purged and replaced by Corbynite apparatchiks with no practical skills in electioneering. Their bizarre ideas included wasting £3m of members’ money on “community organiser” jobs for their mates. Nobody seems to know what they were actually doing – and that money could have been spent on election organisers.

Precious months of election preparation time was spent trying and failing to deselect MPs who ended up focused on winning their trigger ballots rather than canvassing electors. At the same time, wildly unsuitable hard-left candidates were imposed – against the wishes of local members – in seats that many of them subsequently lost.

Again, in 2015, I wrote: “Our performance in London was almost what was needed nationally to get somewhere near victory. This reflects excellent organisation and high membership … But it also reflected the coalition we had chosen to assemble nationally.

“The lamentable 35% strategy envisaged scraping together a coalition of Guardian-reading liberals many of whom had hated our previous government, ethnic minority voters and people on benefits who had been on the receiving end of Tory austerity and welfare reforms. In London where these three groups are increasingly large segments of the electorate, this was enough for a great result. Outside London and ‘Guardian-land’ seats like Hove and Cambridge these groups of voters are simply not numerous enough in marginal seats for us to win.”

We doubled down on this, too. I concluded in 2015: “It wasn’t just our policy package that didn’t speak to swing voters, culturally we find it almost impossible to connect with them. Our leading politicians, MPs, councillors and members increasingly look and sound like a particular cultural milieu that is deeply alienating to the kind of normal people we need to win over. Basically we look and sound like Guardian-land. When voters have legitimate concerns about abuse of the welfare system we react sniffly, dismissing their own lived experience as prejudice. We have at least started to accept concerns about immigration are legitimate and not bigotry, but we have a long way to go on regaining trust when they know it was us that allowed early mass movement from central and eastern Europe.

“I never got any sense from our campaign that we liked or cared about the median voter in the key seats, the family in work, in good health, with a mortgage, working hard and trying to do better. Our 35% strategy didn’t include seeking any switchers direct from the Tories so we didn’t get any.

In the absence of us seeming to want back anyone who had gone from Labour to Tory in 2010, those of this group who had become angry with the Tories, plus the most culturally alienated segment of our 2010 working class core vote, went somewhere else, to someone who did seem to want them.”

We didn’t listen to them then. Labour went off and indulged for four years in a fantasy about transformational socialism, led by an uncharismatic, inexperienced extremist with not an iota of empathy or connection to mainstream voters.

This may be the last chance we get to listen to the people. There is no alternative electoral force on the centre left – Labour is the only alternative government to the Tories. Even with the advantages for them on the Brexit debate and the two main parties vacating the centre ground, the Lib Dems have made no advance.

If we don’t want perpetual Tory government, we have to rebuild Labour. We need to persuade people who share our social democratic values and desperately want a centre-left government focused on social justice that they need to join or re-join Labour and be part of the struggle to make the party decent and electable again.

The road back from this will be longer and steeper now. We may be looking at ten more years in opposition. We will need to build a coalition broad enough to win even if the Tories bring in boundary changes that set us back even further, and even if Scotland leaves the UK and those previously Labour seats are lost forever.