For once, Labour has been quick off the mark. It is only 10 days since the party lost a fourth consecutive general election and it is already preparing for its next defeat.

Despite the obvious truth that Jeremy Corbyn must take the blame for the worst result in almost 100 years, Rebecca Long Bailey, his anointed successor, is the favourite to succeed him as party leader. Her election would be the public statement that Corbyn has gone but Corbynism lives on.

Labour supporters, who want to win the next election, should not despair. The party’s future success, perhaps even its survival, depends on the genuine democratic socialists in the parliamentary party seizing control of the political agenda. The elevation of Long Bailey would provide an early opportunity to demonstrate that they mean business.

The cause would be best served by an outright refusal to accept the imposition of a leader who does not command their confidence. A formal protest with a recorded vote would be almost as effective. Emboldened, they must then insist that the shadow cabinet is, once again, elected – giving its members an independent authority that they would not possess as the leader’s nominees. With their status restored, they would be free to challenge the strategy and tactics of both the leader and the advisers who, with Corbyn, must take some of the blame for the bloodbath of “black Thursday” and are, even now, arranging to remain surrogate leaders in the new regime.

Labour MPs are notorious for their reluctance to fight the ideological battle for democratic socialism. The common response to the complaint that they have watched, but not opposed, the triumphant progress of the far left is the claim that at least they “stayed and fought”. More often than not, they stayed without fighting.

Jeremy Corbyn in September 2015, as he was announced as Labour leader. Photograph: Stefan Rousseau/PA

If they fight now they will, of course, be accused of splitting the party. In truth they will be preventing, or at worst postponing, the real split that is bound to follow a further drift to the unelectable left. The second accusation will be the creation of a “party within a party”. A distinct and separate party of the far left has been a cuckoo in Labour’s nest ever since Ed Miliband’s invention of cut-price membership. Men and women who had spent long, dark nights outside Labour meetings hawking revolutionary newspapers came in from the cold – bringing their sectarian intolerance with them.

They became the pathfinders for the most extensive and, it must be admitted, most successful takeover bid in Labour history. At its heart was Momentum, which began life under the guise of Corbyn’s Praetorian Guard but swiftly evolved into a vehicle for moving the party to what turned out to be the unelectable left. Momentum infiltrated constituency parties, enrolled enough delegates to successive annual conferences to gain a stranglehold on party policy, took effective control of Labour’s national executive committee and attempted – with a measure of success – to “deselect” Labour MPs who did not share its prejudices. Momentum found natural allies in recent conversions from Marxist and Trotskyite factions who, encouraged by the hope of colonising a real and functioning political party, suddenly saw the light.

Compared with Momentum, the Militant tendency – which attempted to subvert Labour in the 1980s – was a ragbag of second-rate conspirators who took corrupt control of Liverpool but were only an irritant in other parts of the country. No Militant sympathisers were employed in the Labour party headquarters or in its regional offices, and no major trade union leader supported Militant’s aims. Now full-time officials openly boast of their Momentum membership. Militant remained an obscure sect.

Thanks in part to Momentum, the Corbyn project was endorsed by thousands of good democratic socialists. The radical rhetoric obscured the fatal flaws of Corbyn’s philosophy – the blanket opposition to private enterprise, the support for any tinpot dictator who called himself a socialist, the intolerance of disagreement, the failure to cleanse Labour of antisemitism which proved that, although he hated racial prejudice, there were some racial prejudices that he did not hate enough. There is no doubt that there is still an army of Labour party members who cannot bring themselves to believe that the Corbyn project was destined to end in disaster. They have to be persuaded that Corbyn’s way could only ever lead to the disappointment of defeat and the betrayal of the millions of families who need a Labour government. No doubt Momentum’s leaders are still rejoicing about the control they achieved over the party machine. The celebrations are not being replicated in the food bank queues that, following Labour’s defeat, will only lengthen.

Rebecca Long Bailey is Jeremy Corbyn’s ‘anointed successor’. Photograph: Peter Nicholls/Reuters

Before the brilliance of Neil Kinnock’s Bournemouth conference speech in 1985 extinguished the hopes of Militant, outriders spent two years preparing the ground for his final assault. For Labour to become a party of government again it needs another army of genuine democratic socialist MPs mounting a similar onslaught on the great ideal’s false friends. Their task will be more than the recruitment of new party members to become a counterweight to infiltrators from the unelectable extremes. They must convince floating voters that democratic socialism is alive, well and ready to wake from its slumbers – and is worth voting for. Thanks to the Corbyn project, few people believe that today.

It may be that the parliamentary party is not in a mood to heed the calls to arms. The self-styled “moderates” have always suffered from an excess of caution. But if there is to be a fight, have no doubt that the real democratic socialists will occupy the high ground.

We are the apostles of true equality and the personal freedom that it must sustain. And we offer the politics of hope – not empty slogans about the better world we hope to build but a real chance of bringing it about. A genuine democratic socialist party can win elections. The time has come to rise up against all who stand in our way.

• Roy Hattersley served in James Callaghan’s cabinet and later became deputy leader of the Labour party