Frank Field saw benefit in the Lib Dems. In this election year, Labour would be wise to do the same | Martin Kettle

David Marquand and Frank Field, both of whom died this week, never sat on the Labour benches together. The professor of politics and the long-serving backbench MP had very different temperaments too, one searchingly academic, the other a bold moraliser. They also disagreed about many of the big issues in British politics, the European Union above all.

But they also had some hugely important things in common. Both started as free-thinking Labour MPs – Marquand in 1966 and Field in 1979. Both possessed a rare degree of intellectual and spiritual hinterland. Both then went on lifetime political journeys. These took them increasingly away from Labour, though they always remained in Labour’s orbit.

Marquand joined the Social Democrats and then moved to academia, while Field ultimately finished his career on the cross-benches of the House of Lords. Both also believed that the many failures of British progressive politics were embedded in its lack of pluralism. Both were radical reformers who believed modern politics and government have failed to keep pace with modern Britain.

All the same, neither of them conclusively threw in their lot with the Liberal Democrats, the party that stands for such reforms. Marquand remained wedded for years to the possibility that Labour could reinvent itself in a more pluralist way, but a combination of New Labour and the Lib-Dem coalition with the Tories put an end to that. Field advocated tactical voting for the Lib Dems in the 1990s – a heresy that is punishable with expulsion by Labour these days, though it was followed by millions of voters in 1997.

Each was nevertheless a totemic figure among those in the progressive tradition in their generation who argued the need for a different kind of politics in Britain. Marquand was the brilliant biographer of Ramsay MacDonald, a lieutenant of Roy Jenkins, then an impassioned defender of the public realm against both Thatcherism and New Labour, and latterly a Welsh devolutionist. Field started as an anti-poverty campaigner, then increasingly became an advocate of welfare state reform.

The two men were part of the progressive penumbra around the Labour party that rejects doctrinaire politics, particularly of the Labour left, but whose hopes that New Labour would find ways of cementing a more lasting and broader appeal were also disappointed. Both were open to new ideas and open to engaging with other traditions. Each championed the need for democratic and institutional reform and for civic and individual engagement.

In the end, it must be said, each of them also failed. Marquand never succeeded in inspiring some new form of common cause between the left and the centre (for which, in other contexts, read socialism and liberalism, statism and individualism or Labour and the Lib Dems) which could transcend the limitations of either party. Field, meanwhile, never managed to build the coalition for benefits reform that he believed necessary as the welfare budget expanded in response to an ageing society and to changing sickness patterns.

Where does responsibility for this failure lie? It must be shared widely. Part of the sharing out, however, involves asking how and why the Lib Dems, and not Labour alone, have failed to provide the answers.

In a political system such as ours, so dominated by the two main parties, there will often be a good reason to defer thinking about the Lib Dems. The Conservatives and Labour are routinely scrutinised and judged, almost to destruction at times. The prospects of some of the smaller parties such as the SNP and the Greens, to say nothing of Reform, and their impact on the major parties’ battle, are also examined with great attentiveness.

But the Lib Dems? Somehow they are like the dog in the Sherlock Holmes story that did not bark. It says something about a party that has been a presence in British politics for so many decades that reformers such as Marquand and Field never pitched their tents inside the Lib Dems’ walls, instead preferring to remain Labour’s candid but marginal friends. And it says something both about the political conversations of the present day and about the Lib Dems themselves that they are so often ignored.

On the face of it, this is strange. The party is doing well. It has won four spectacular byelections in the past three years. It has the support of one in 10 voters in opinion polls. It may well improve that to one in five or one in six in the national equivalent vote share, which will be the key electoral indicator to watch for after next week’s important local elections.

If that happens, the number of Lib – Dem MPs in the next parliament may even double. Fourteen years after the coalition with the Tories, the Lib Dems now proclaim themselves an anti-Tory party. Activists talk of the mood feeling like 1997, when Paddy Ashdown returned at the head of 46 Lib-Dem MPs, thanks in the main to tactical voting against the Conservatives.

That would be a big advance and a feather in the cap of the party leader, Ed Davey. But what would actually change if Labour also had a large majority? If Field had lived to see a new Labour government, it is not hard to see him making common cause with Davey in opposing Labour’s retention of the two-child cap on family benefits. The Lib Dems may even win their campaign.

But this is a long way from the major realignment and reinvention of the progressive wing of British politics that Marquand always wanted, which has moved in and out of focus since the 1980s. As long as they fight like dogs over the bone, wrote this paper’s editor CP Scott before the first world war, the Liberals and Labour risk the danger that the Tories will come and snatch it back from both of them. That was true then. It is still true now.