This weekend’s defeat in the Labour leadership election brought to an end four-and-a-half years of Left leadership of the party. It was a period when socialist ideas achieved their widest audience in a generation, gaining considerable popularity, and raised the hopes of millions that a fundamental transformation of Britain’s political and economic life was possible. Sadly, it ended in successive defeats – firstly in December’s general election and then Rebecca Long-Bailey’s loss.

In recent days we have seen the Starmer leadership set out its stall for the future direction of the party. The shadow cabinet finalised yesterday reflects a shift to the centre-left, including many decent social democrats but with a significantly diminished role for socialists. This was to be expected, especially after the scale of Starmer’s victory. It is to be hoped that this new shadow cabinet represents the best of the social-democratic tradition, one that brings with it a zeal for reform – but it’s clear that its challenge to the power of organised wealth in Britain won’t match the one laid down in recent years.

For the Labour Left, now is a time for reflection and renewal. As Tribune argued in recent days, socialists should stay in the Labour Party – with its mass membership, its trade union link and its left-wing members of parliament, it remains the best hope of organising a fighting working-class politics in Britain in the years to come. This task must be undertaken alongside serious efforts to rebuild the unions and movements outside of parliament. If one of these paths is followed to the exclusion of the other it will leave the Left politically and industrially worse off, and further isolated from the communities it aims to represent.

But the question of what a Labour Left should look like after Corbyn has not been well explored. The reality is, for all of the achievements of the Corbyn project, it remained institutionally weak throughout its years in the Labour leadership. Momentum – the faction formed from the Jeremy for Leader campaign – embodied many of Corbynism’s failings. It came to represent a London-centric, largely liberal and student-oriented politics which, while successfully harnessing some of the energy of younger Corbyn supporters, failed to develop the project politically and resulted in an operation that often resembled an NGO rather than anything socialist.

To some extent, the process that led to this outcome was difficult to avoid. From its earliest days Momentum was commandeered into the defence of the Corbyn leadership and adapted its structures according to these short-term political aims – which mitigated against the development of a more effective socialist organisation. It leaned into Corbynism’s strengths among younger activists in large cities, particularly in London, in an effort to amass forces which might buttress the leadership. But in the process it came to represent much of the project’s weaknesses among working-class communities in other parts of the country.

Through the pressure to achieve immediate goals, Momentum developed in an uneven way. While at times delivering impressive results in internal elections, many local and regional groups felt ignored and treated as fodder by an unelected office in London that offered little leadership, but held an influence over the organisation’s political direction as significant as its elected National Coordinating Group (NCG). Criticisms of the decisions which led to this outcome are fair, but they must also recognise a reality: Momentum was trying to develop a structure in a short period which broke with decades of ineffectual practices on the socialist Left while also mounting a defence of a besieged leadership. This was by no means an easy task.

However, it must now be recognised that this short-term orientation has left our movement institutionally weak as we face the challenge of rebuilding after Corbyn. This is not a problem that applies only to Momentum – in parliament, the Socialist Campaign Group was recently revived but is not yet an effective force. Nor is it connected to the wider Left in any meaningful way. The other pillar of the Labour Left, its union link, is historically strong, with many left-wing leaderships. But here, too, Corbynism failed. It did not contribute to the revival of the unions that is a necessary precondition of rebuilding class politics. The years since 2015 have neither seen a significant increase in union membership nor any shift in the industrial terrain which might embolden workers to fight and win in their workplaces.

The Labour Left, in other words, must be renewed. The difficulty in such efforts, especially at moments of defeat, is their tendency to result in recrimination and fragmentation. The only hope that the Labour Left has of asserting itself in the coming years rests in finding a unity of purpose which builds a formidable socialist voice in the party, one capable of pushing back against turns to the right, defending the policy platform and empowering members to ensure the party does not become mired in the world of Westminster. Criticisms of Corbynism’s failures must be made – but they must be made in a comradely spirit that recognises the collective responsibility of the movement for the defeats we have endured.

The path to a renewal of the Labour Left runs first through Momentum, which will soon be contesting its National Coordinating Group elections. Any programme for change must reflect the weaknesses detailed above. For a start, a revived Momentum must be socialist in its perspective. That means a much greater political quality to its messaging, which has at times been infuriating. Public roads and police forces exist in every country in the world – they are not socialist, and no amount of condescending videos will convince people otherwise.

But it is not just a question of communications. Momentum must take seriously the need to represent all parts of Britain and break with its London comfort zone. The political impacts of this myopia have been enormously damaging. During the general election, the organisation threw unjustifiable amounts of resources into capturing London seats with significant Tory majorities for high-profile candidates. Meanwhile, the support for MPs attempting to defend vulnerable Leave seats (let alone make gains in the North) was negligible or too little, too late.

Similarly, Momentum must orient itself to working-class people of all ages, and away from a narrow focus on the young and university-educated. Corbynism in general failed as a project because too few people in too few places felt an ownership over a programme that would have radically improved their lives. The last election exposed how narrow Labour’s coalition under Corbyn had become, and the gulf that exists between organisations like Momentum and working-class communities across the country gives an insight into why. There are significant structural issues here, such as the reliance Momentum (as well as aligned organisations like The World Transformed) has placed on activists whose personal circumstances afforded them the opportunity to volunteer full-time in London. This is, to put it mildly, a small pool of people.

To their credit, the development of local groups operating on their own terms under the Momentum and Transformed brands has brought about a degree of political education that was previously lacking in the movement. However, it has been nowhere near extensive enough. A revived Momentum – with a socialist political direction – must take this task seriously. It must see political education as a question of developing members’ capacity to build class politics in their own communities and play constructive roles in the wave of struggles which the coming recession will produce.

It is an awareness of the scale of this impending economic crisis that makes both Momentum’s renewal and its commitment to a united approach on the Left of crucial importance. Momentum must reform, acting in the strongest possible unity with left-led unions and socialist MPs, with the aim of developing a Labour Left which can speak with one voice when the most important battles arrive. Otherwise it will be rendered powerless both in the party and in wider society.

Writing about the lessons of economic crises for the Left, Aneurin Bevan said that “boldness in words must be matched by boldness in deeds or the result will be universal malaise, a debilitation of the public will, and a deep lassitude spreading throughout all the organs of public administration. Audacity is the mood that should prevail among Socialists as they apply the full armament of democratic values to the problems of the times.”

That boldness is called for today. Corbynism inspired many of us, and had significant achievements. But it has been defeated. We face a historic economic crisis, a climate emergency, a rising far-right and a hollowed out democracy with rapidly increasing inequality. Moderate forces will not be sufficient to address the scale of these challenges. We need a renewed socialist Left capable of raising systemic alternatives and harnessing the power of working people. The task of building it starts today.