One could be idiosyncratic. Two might be a coincidence. Four and with more to come begins to suggest a pattern. Were Tristram Hunt the only example of an ambitious and talented politician in his 40s contemplating his life and deciding there were better things to do with it than continuing as a Labour MP, his decision to abandon parliament would be interesting but not wildly significant. When the offer to become director of the Victoria and Albert Museum was confirmed, I bet it took him less than a nanosecond to decide that this would be a whole lot more rewarding – and not just in the financial sense – than remaining as Labour MP for Stoke-on-Trent Central. He is and has always been entirely out of sympathy with Jeremy Corbyn and what the current management of Labour is doing to the party.

His witty sallies mocking Corbynism were the mask on a deep despair, widely shared by Labour MPs, about their prospects. Before he announced his decision, he had told friends that he would wake up in “a cold sweat”, haunted by the spectre that he would one day find himself a decade older and still sitting on the opposition benches. He was a passionate and eloquent advocate for the Potteries and their people, but he came into politics with aspirations to do more. His majority was too slim to be confident that he could survive the disaster that will engulf Labour if the party’s current opinion poll ratings are translated into a crushing defeat at a general election.

The hard left has been very active in his constituency and had him on its hitlist. On top of which, the boundary commissioners have proposed that his seat should be abolished. His choice was to wait to be handed a redundancy notice or take what he describes as “a dream job” running the V&A. It was not really a choice at all.

What gives this departure a wider resonance is that his is not an isolated case. It follows Jamie Reed’s decision to quit his Copeland seat to become head of development and community relations at the nuclear reprocessing plant in the constituency. Other MPs are also telling us that they think there is no foreseeable future for Labour as a party of national government, or even as an effective and relevant national opposition, by clambering into lifeboats provided by civic politics. Andy Burnham will stand down from parliament if, as is likely, he succeeds as Labour’s candidate for mayor of Greater Manchester. Steve Rotheram will resign his Liverpool seat if he fulfils his goal of becoming mayor of the city.

Tristram Hunt had often said that he thought Labour was on a suicidal course and had been targeted by Corbynistas for a revenge deselection. Jamie Reed could never be confused with an enthusiast for the current Labour leadership. But it is wrong simply to categorise the exodus as the abandonment of Jeremy Corbyn by people who have never liked him or his brand of politics and have always been convinced that it means calamity for Labour. Mr Rotheram is the Labour leader’s parliamentary aide. He can hardly be branded a serial disloyalist. Mr Burnham, though no Corbynista, was one of the very few members of the shadow cabinet who did not resign last summer and he opposed the failed attempt to oust the leader. Mr Hunt was consumed by feelings of dread and frustration much more profound and complex than a simple animus towards the party’s leader. His resignation letter expressed a general lament that the left, including the centrist left that he represents, have failed to respond to the challenges thrown up by “social, cultural and economic forces which have rocked mainstream social democratic and socialist parties” across the democratic world.

Will others follow his example? “I think it is inevitable there will be more,” says one very well-placed observer in the parliamentary Labour party. Most Labour MPs will stick it out and pray something will turn up to save the party and their skins. Some will do so from the conviction this is the right thing to do and some will not quit parliament because they don’t have good alternatives. Not every Labour parliamentarian has a curriculum vitae that would make them a candidate for a city mayoralty or the leadership of one of the world’s great cultural institutions. But I have heard many rumours about Labour MPs who are thinking about deselecting themselves from parliament and I know quite a few who are in a state of personal crisis about their futures. Every time a Labour MP announces that they are off to do something else, it sharpens the questions others ask themselves during dark nights of the soul. Yes, this is often the product of alienation from the current leadership and career disappointment. That doesn’t stop it also being a very human story: people asking themselves whether they want to spend an indeterminate and possibly endless number of years in miserable frustration, out of government and powerless to do anything for the people and causes they care about.

The decline in the prestige of parliamentarians, and public respect for them, comes into it as well. Shortly before Christmas, one Labour MP, a man of ability who once fizzed with relish for politics, confided that he was looking for a fresh career, saying: “I have to ask myself – and I know a lot of colleagues who are doing the same – whether this is how I want to spend the rest of my life.”

The responses to Mr Hunt’s departure have been instructive. Corbyn loyalists have reacted exactly as you would expect them to react by saying the party will be better off without him. Good riddance to a “Tory-lite”, a “Blairite” and a “careerist”. That has been the wholly unsurprising reaction from that entirely predictable quarter. The response from people in the Labour mainstream has been more diverse. There is genuine disappointment among some MPs, especially those who admired his efforts to try to engage intelligently with the questions raised for social democrats by the new forces sweeping politics. Regret is mingled in some cases with envy that he has found a golden parachute to escape the burning plane. Then there are fellow Labour centrists who are angry with him for deserting the field of battle. They are the people who are really cross with Mr Hunt.

Some fear that this high-profile departure will demoralise Labour moderates and just at the moment when there were some reasons for them to be encouraged to believe that the tide might be turning. Momentum, the activist organisation set up to cheerlead for Mr Corbyn, has become riven by poisonous schisms between different factions of leftists. Len McCluskey, the general secretary of Unite and Mr Corbyn’s most pivotal supporter in the union movement, is facing a serious challenge for his position from Gerard Coyne. As for the attempt to stage a new year “relaunch” of Mr Corbyn, even his best friends can distinguish between that and a resounding success.

It is perhaps most significant that his inner circle appear to have abandoned their plans, at least for the moment, to try to strengthen their power within the party. Last autumn, they said there was going to be a special session of the party’s national executive committee, a “democracy day”. The idea was that this would pave the way for changes to the party’s rules that would strengthen the power of the Corbynistas within Labour. This plan has been quietly dropped. The special NEC meeting has never been convened, presumably because they aren’t sure they can command the votes to get the changes they want.

Developments at a constituency level have also been more encouraging for the moderates. As I reported to you before Christmas, non-Corbynites have been prevailing at annual general meetings of local parties by securing key posts in constituencies. This matters, not least because this is the first line of defence against attempts to deselect MPs. Since I last reported to you, I’ve collected more examples of how these local struggles are playing out. A striking one comes from the London constituency of Vauxhall. Paul Mason, one of Jeremy Corbyn’s most prominent media advocates, stood for a position on the local party’s general committee. He was defeated. By a delicious irony, he was beaten by someone who used to be a member of the SDP, the now defunct party that split from Labour when it lurched to the left in the 1980s.

So the harshest reaction to Mr Hunt has come not from Corbynistas, but from his fellow Labour centrists who think he has let them down. Some admonish him by citing Hugh Gaitskell’s historic instruction to Labour moderates that they should “fight and fight again to save the party we love” – not abandon the struggle in the heat of the battle for a lovely job at a museum.

To friends who have rounded on him, he has responded that he entirely understands their anger. He also told them that, having devoted a lot of time to thinking about how to renew social democracy for the 21st century, he had grown increasingly fearful that he hadn’t got the answers to Labour’s predicament. Of all the reasons for his departure, that is the most telling and, for anyone who wants the party to have a future, the most disturbing.