Yet again, there is breathless media speculation about defections by Labour MPs to either sit as independents or form a new party. I understand that some MPs and many ordinary members are at the end of their tether. Many feel that something drastic is the only moral response to an unbearable situation – whether over the failure to tackle antisemitism in the party, the ambiguous stance on Brexit, partisan deselection threats to MPs and councillors, abuse, bullying and uncomradely behaviour in meetings and on social media, lack of confidence in the leadership to govern, or a combination of all of these factors.

I do not underestimate the darkness of the situation. My professional involvement in campaigning on Israel means I’m exposed every day to the alienation, distress and fear being caused to the Jewish community by antisemitism. As secretary of Labour First, I track the state of CLPs and selections around the country. As a prominent moderate on social media and running for the NEC, I have first-hand experience of receiving online abuse.

But quitting is not a serious tactical or strategic solution to the political situation Labour moderates are in. It’s more like, to quote Nye Bevan, “an emotional spasm”. An understandable reaction that may salve the consciences of the people involved, but one that will make things worse not better for the politics they espouse.

Assuming there are MPs thinking about leaving, and it isn’t all a figment of journalistic imagination, even their own briefings to journalists cite just 12-20 departures. This would hurt Labour, but it wouldn’t cause a realignment in British politics. A party with 258 MPs, 40% of the vote and 500,000 members isn’t going to face an existential challenge from 12-20 MPs going, let alone resignations of ordinary members.

The pathos of the situation is the confused briefing about what form the departure would even take, with a lack of clarity about whether this would involve sitting as independents, as an organised independent group, or as a new party. The SDP at least had a plan, three charismatic household-name national leaders and a fourth man, Bill Rodgers, who was one of the best organisers of his generation. It still failed because, then as now, the bulk of Labour moderates, and the unions, wanted to save Labour, not kill it. Along the way the SDP discovered that swapping the left ground for the centre ground did not mean you escaped from the attentions of obnoxious grassroots activists with silly views about Israel and unilateral nuclear disarmament: they just swapped the Labour version for the Liberal version, replete with beards and sandals.

Not only has every centrist breakaway from Labour ended in failure, the lesson from the recent history of the hard left is the same. It was people who stayed through the Blair years like Corbyn who have been vindicated, not people like Scargill who walked out and founded micro parties. What every departure has in common is that it weakens the moderate cause within Labour and delays the day when the party will be restored to decency and mainstream politics.

Every MP who leaves is giving a free pass to Momentum to select a hard left successor to Corbyn. MPs who have defected have hardly ever held their seats as an independent or third party candidate, however strong their personal vote. Of the 28 Labour MPs who defected to the SDP, only five survived the next general election. The net impact will be to shift the PLP to the left, to make it easier for hard left candidates to get nominated in future leadership contests, to make it easier for the leadership to fill frontbench positions with their supporters, to reduce the chances of the PLP stopping wilder policy excesses passing through the Commons, to remove for moderates the grassroots leadership seen in a CLP where the MP is sound.

In councils, unless a majority of the entire council defects at once, quitters are walking away from local power, which in almost every Labour council is being exercised sensibly. They would be entering the impotence of the opposition benches whilst again giving Momentum a free pass to pick their successors.

Every individual member who leaves is one less vote for moderates in NEC and other one-member-one-vote elections, and if they are active enough to attend meetings, one less vote for moderates in electing conference delegates, CLP officers, council and parliamentary candidates. Given that the conference decides the rulebook and the NEC and NCC decide its implementation, it specifically weakens the fight against antisemitism if there are fewer moderate members to vote for control of those bodies.

Britain’s first-past-the-post system tends to lead to two rival parties of government – the Tories and Labour. If the latter is split or weakened, our electoral system means the Tories dominate. Given their current extreme and ineffective record, it is not in the national interest to allow them to win power by default.

The Labour Party is one of the most magnificent institutions in Britain’s history, responsible for so many great progressive achievements: the NHS and welfare state; NATO; race, women’s and LGBT equality legislation; devolution for Scotland and Wales; the National Minimum Wage; record investment in schools and hospitals. Are there really people on Labour’s historically mainstream wing who have so little stomach for the fight to restore Labour to its best traditions that they would walk away from 115 years of achievement because of three years of pain?

It’s our party and we should fight to save it. This is the fight of our political lives, saving Labour and restoring it to decency is the most important thing any of us can do for our country’s future. You don’t quit at the start of that kind of fight. You don’t stop until you have won.

If you owned a beautiful historic house that until three years ago had been a happy home, and squatters moved in and trashed it, you wouldn’t walk away and build another, far smaller house, or kip in a tent in the local park. You would fight to get it back.

We need the MPs who care about having a decent centre-left party in Britain to fight to save the one we already have, not quit and leave us in the lurch to fight on weakened – and, worse still, forced to fight them in elections. That is what it would come to: Labour moderates having to electorally destroy their former allies because removing a rival centre-left party would be a precondition of removing the hard left from power within Labour and thence taking Labour back into government.

In his latest column, Dan Hodges quoted an MP saying: “The problem is those MPs like Tom Watson and John Spellar who think this is just a rerun of the 1980s. They think all we have to do is keep our heads down for ten to 15 years, and then everything will sort itself out.”

I don’t think they do think that. It’s not a rerun of the 1980s – it’s a far more profound crisis. And you know what really is outdated 1980s thinking being rehashed? Setting up an SDP re-enactment society to make the same mistakes again. To quote Marx, “the first time as tragedy, the second time as farce”.

In any case, the MP concerned must never have read John Golding’s book ‘Hammer of the Left’. If he had, he would know Spellar – far from keeping his head down – was organising flat out to win the party back throughout the ‘80s. Dan wouldn’t remember as he was on the left of the party in his youth.

I don’t want moderate MPs to “keep [their] heads down for 10 to 15 years”. I want them to lead, to organise and to help create moderate structures to take on Momentum. Lead in their CLPs so that they recruit good new members, get reselected, get their councillors reselected, get good CLP officers elected, win nominations for national elections, pass good policy motions, send good delegates to conference.

I want them to lead nationally with generating new ideas, giving new hope to members and potential members who share their values, developing a modern policy agenda. I want them to speak on TV and on the radio, to have letters and op-eds and columns pouring out our message. I want them to lead in all the other CLPs that don’t have a moderate Labour MP – where are the moderate equivalents of Chris Williamson charging round the country rallying the troops?

I want them in the future to be able to look back and say it was tough, it was horrible, but they were part of the generation that saved Labour so that it could save the country. If they want to look back and say they left politics not with a bang but a whimper, and in doing so took Labour down with them, they can do it without me.