Contrary to popular belief, most politicians are fundamentally decent. Professionally, I come into regular contact with MPs and peers, and find most are in it for the right reasons, not for glory or power. 

Across every party, they aspire to help constituents in desperate situations access key services, to improve transport links, or build a fairer society. Housed in unglamorous offices and with overflowing postbags, facing interminable social media abuse, they work long hours to change, if not the world, then their slice of it.

Which is why I know that for Labour’s remaining moderates — those for whom New Labour was a high not a hiccup — these last four years have not been smooth sailing. 

I don’t have to name names but you know who I mean; the ones who crop up criticising the latest antisemitism scandal, the ones who backed Owen Smith. Those for whom Corbyn’s social media warriors cannot conceal their venom. The ones rumoured to be joining Change UK who never quite did. The ones in an impossible bind.

Some misguidedly backed Jeremy Corbyn to “widen the debate” but sticking with Labour under his stewardship won’t have been easy. Every headline about its confused Brexit stance, every ignored instance of antisemitism, every time the opposition’s approval ratings fell through the roof, will have left them miserable and frustrated.

They have my sympathy. It’s not easy to leave something with which you have a lifelong allegiance; imagine asking a football supporter to switch teams. 

But with recess ending and an election looming, it’s crunch time. 

For years they have been looking away, pretending not to see what was right in front of them, like a scorned wife aware of her husband’s infidelities, staying in the marriage for the kids. They can look away no longer. 

If in 2017 they could legitimately campaign on the basis nobody expected Labour to win — a vote for me isn’t one for him — we know now, after repeated polling failures, anything can happen. 

We know that if these MPs stand on our doorstep asking for our votes they are, ultimately, asking for us to put Corbyn and McDonnell into Britain’s seats of power. They are asking us to give the keys to Number 10 to politicians who either cannot or will not see bigotry for what it is; who have consistently failed to mount a clear stance on the defining issue of our era. 

They are asking us to hold our breath and vote in a man who refuses to answer intrusive questions from journalists and has demonstrated a consistent record of cosying up to people with ideologies at best described as questionable. 

Perhaps most importantly, we also know — because they have hardly been silent on their leader’s shortcomings —that while they may back some of his policies, they don’t actually regard him as a credible or safe choice.

But as I said, most politicians are fundamentally decent. So four years on, now is the moment for Labour’s centrists — and indeed, the motley crew of Tories who abhor their leadership, but that’s another column — to show where they stand. To put principle above the pursuit of power, popularity or professional advancement.

When Chuka Umunna joined the Lib Dems he was mocked for having been in three parties in almost as few months. But for those who have jumped ship, it’s no easy option. Most face tough electoral battles and may well lose their seats.

Yet in doing so, in making the more difficult choice, they set an example for their peers.  

Some Labour moderates stayed, contending they could change things from the inside. That strategy might have convinced four years ago, but its hollowness is painfully apparent today. Valid though criticisms of the current Government may be, can they really argue a rotting opposition is a preferable option?

And if the rule of British politics is that elections are won by the main parties, little today suggests old certainties will hold. Post-Brexit, we are surely set for years of fluctuating politics. 

Thus, there is everything to play for, whether they join Jo Swinson’s ebullient Lib Dems — a party I never imagined I’d support, back in the days when David Ward was the left’s most egregious character — or strike out as independents.

Allegiances are shifting. Research has shown millennials and centennials have less tying them to specific parties. The young today care about housing, the environment and social issues, not whether they are backing the party their fathers backed. 

There is opportunity here for those willing to gamble on seizing it. 

Yes, Change UK has been a flop; no, a convincing challenger party has not yet emerged. Perhaps it will in time, perhaps not. 

But either way, the clock has run out for Labour’s decent, admirable, fence-sitting moderates. 

They must make a choice. And if it costs them their political futures? At least they’ll go down as having tried.