If you are going to blame your failings on someone else and hope to sound plausible, it is usually best to stick to just the one excuse. Turn up late for a job interview and there’s a chance of receiving a sympathetic hearing if you put it down to a delay to your train. Blame it on a delay to the train and the child who hid your house keys and the dog which ate your best suit and the conspiracy masterminded by Lord Voldemort who has been ruining your life since you were born and the proliferation of the excuses will render them all incredible.

The dwindling band of apologists for Jeremy Corbyn can’t even get their alibis straight. According to Emily Thornberry, the leader’s constituency neighbour in Islington and shadow foreign secretary, the party’s cataclysmic loss of the Copeland by-election is to be blamed on “fake news”. According to Richard Burgon, a Corbyn lieutenant in the shadow cabinet, the Cumbrian seat had always been “marginal”. For sure. It had previously swung to the Conservatives as recently as 1931. The shadow chancellor John McDonnell told the BBC that the culprit was Tony Blair, even though he is an utterly discredited figure, or so the Corbynistas have always previously told us, and left office more than a decade ago.

Others in the leader’s coterie point the finger at Labour MPs for failing to demonstrate sufficient enthusiasm. If only they’d quaff the Kool-Aid and proclaim that he was marching them towards power, all would be dandy. Ian Lavery is the leader’s recently appointed elections co-ordinator. Bad luck, Ian. According to him, the Tories triumphed because the public don’t like politicians in general – apart, of course, from Mr Corbyn, who is “one of the most popular politicians in the country”.

I’m not sure which country Mr Lavery had in mind. Perhaps Mongolia where they may not be very acquainted with Mr Corbyn. Perhaps not Britain, where he is breaking post-war records for unpopularity with a net approval rating knocking around minus 40.

My favourite excuse came from the man himself when Mr Corbyn claimed that Labour lost the Cumbrian seat because cross voters feel they “have been let down by the political establishment”. Well, of course. Angry revolt against the establishment is a perfectly logical explanation for why Copeland will now be represented by an MP from the Conservatives, the party that has been in government for the past seven years.

When he became Labour leader, Jeremy Corbyn promised his followers that he would do politics in a new way and I guess he has delivered that, if not quite in the way those who put him there may have anticipated. In the old politics, it was a boringly reliable rule that the main party of opposition could be expected to hold seats that it was defending at by-elections, usually with an improved vote share. In the new and thrilling world ushered in by Mr Corbyn – well, it is new and thrilling if you are a Tory – voters in a historically Labour area are now galvanised to turn up at the polling stations to hand the seat to a totally delighted Theresa May.

There is simply no way of glossing the Copeland result as anything but a catastrophe for Labour

There is simply no way of glossing the Copeland result as anything but a catastrophe for Labour and a tolling bell warning to the party about the fate that awaits it at a general election if it doesn’t adjust trajectory before it is too late. Mrs May has been gifted the first by-election gain for a government since 1982, when the Tories won Mitcham and Morden in the very special circumstances of the Labour-SDP split and the Falklands War. That was the prelude to a historic Labour collapse and a crushing Conservative landslide at the general election the following year. Even at that 1983 “suicide note” election, Labour’s post-war nadir under Michael Foot, the party managed to hang on in west Cumbria. Were the swing against Labour to the Tories in Copeland to be replicated across the country at a nationwide election, Labour would be reduced to well under 200 seats and Mrs May would be returned to Downing Street with a Commons majority in excess of 100, a prospect which is reviving chatter among Tory MPs about trying to engineer an early election.

The blame cannot be put on Labour’s local standard bearer, an able candidate who did her energetic best to exploit a hot local controversy about the future of a maternity unit in the constituency. One Labour leaflet shouted: “Babies will die.” Even that shroud-waving couldn’t save the seat. Grim wags in the party’s ranks are now darkly remarking that folk in Copeland would rather let new-borns die than endorse Corbyn Labour.

It is only superficially better news for Labour that its candidate in Stoke-on-Trent Central managed to cling on against a challenge from Ukip that turned out disastrously for that party’s new leader, Paul Nuttall. The Battle of Britain ace, multiple Oscar winner and inventor of the internet who earned 200 caps playing for England, spent much of his campaign having to deny that he is a serial fantasist. Even with an imploding campaign fronted by an incredible leader, Ukip stole some vote share from Labour. So did the Tories. The Labour vote share was marginally lower in Stoke than it was in Copeland and considerably below the combined vote of Ukip and the Conservatives. The difference with Copeland was that the anti-Labour vote coalesced behind the Tories in Cumbria while it split in Stoke. Conservatives are pleased that Labour hung on in the Potteries on the basis that Jeremy Corbyn’s life expectancy as leader might have been shortened if his party had lost both seats.

It has become fashionable to say that Labour’s problems “go deeper than Jeremy Corbyn”. I agree. They do. But that form of analysis is a trap for the party when it is deployed as another false alibi. Just because he is not the only problem does not mean that he is entirely incidental to Labour’s agonies. Canvassers from all parties report that his name was constantly raised on the doorstep by ex-Labour voters either as a reason to switch their support elsewhere or for them to protest in a quieter way by staying at home. There was a reason that Mrs May went campaigning in Copeland, unusual for a prime minister and vindicated by the result, and there was a reason that Mr Corbyn stayed away in the latter stages of the campaign.

While a shock, this should not be a surprise. Certainly not to anyone who has been paying any attention to the opinion polls. The most recent survey from YouGov has Labour an alarming 16 points behind the Tories.

ICM makes the deficit even more enormous at 18 points. There is no comfort to be derived from the notion that polls can be incorrect. When they have been misleading before, the polls have been wrong in a way that made Labour seem more popular than it actually was.

Mr Corbyn’s internal position is clearly eroding. The trades unions are getting restive as they finally face up to what unopposed Tory government means for their members and their families. Dave Prentis, the general secretary of Unison, previously an endorser of the Labour leader, complains that the party is “sliding towards irrelevance” and “hasn’t moved an inch closer to Downing Street” under its current management. You have to be very obtuse if you can’t now see how hollow was the promise that a Corbyn leadership could build a “social movement” that would sweep the country.

At Westminster, the Corbynistas are factionalising. One-time allies in the shadow cabinet are manoeuvring

The Tory-enabling position taken on Brexit has spread further disillusion at the grassroots. At Westminster, the Corbynistas are factionalising. One-time allies in the shadow cabinet are manoeuvring as if they expect a leadership vacancy before the next election. The number of Corbynista cheerleaders on social and other media is dwindling. That loud thud you can hear is the sound of scales falling from previously adoring eyes as they finally begin to confess to themselves that their saint is made of plaster.

This does not mean that anything is likely to happen in a hurry. Action by the unions, if it occurs at all, waits on the outcome of the struggle for control of Unite between Len McCluskey and his challenger, Gerard Coyne. The parliamentary party remains paralysed. Speaking in Scotland yesterday, Tom Watson, the deputy leader, correctly observed that “seven years into a Tory government, we shouldn’t be facing questions about whether we can hold the seats we already hold … holding what we have is supposed to be the easy bit.” But he went on to say: “This is not the time for a leadership election.” After their miserable failure to dislodge him last summer, Labour MPs are not ready to have another go at ousting Mr Corbyn. Though many are fearful that the damage to the party will be deeper and more lasting the longer this tragedy continues, they are even more scared that a further challenge would backfire. Most are still sticking to what I have called the Shut Up Strategy, also known as the Give Him Enough Rope Strategy.

So Labour remains trapped with a leader who blames his failings on everyone but himself. And the country remains stuck without a functioning opposition at a time when it has never more needed one.