In my pre-parliamentary days, when I helped shape Shell’s future business strategy through scenario planning, a psychological technique my team used was trick pictures showing totally different stories depending on how one perceived them. They are a good metaphor for current UK politics.

Looked at in one way there is stasis: the - supposed - return to two-party politics defined by tribal allegiances. A century-long ideological struggle between proponents of capitalism and socialism embedded in the Conservatives and Labour.

Seen from another angle, there is political ferment and radical uncertainty. The two traditional parties are riven by internal conflict; dissident MPs treat their party leadership with open contempt.

New parties are springing up. There have been three major elections in three years (four in Scotland and Wales), opening up divisions based on geography and generation as well as class and belief.

These contrasting pictures are reflected in the issue dominating public life: Brexit. On the one hand, it is tiresome, negotiations proceeding at glacial speed. On the other, it is inspiring extremes of rage and hope.

Nor is the story about Britain alone. In the decade since the financial crisis destroyed widely-held assumptions that living standards would inexorably rise, populism has proliferated. In systems with variants of first-past-the-post, populism has operated within existing two-party models, notably in the US, India and (so far) the UK; PR-type systems have generated new parties and movements (Italy, Germany, Spain, France). Popular frustration breaking political moulds.

As the leader of a party which is both very old and very new (long-established but with a growing, young membership), my job is to navigate a way through this confusing landscape.

The first, essentially stable, picture of British politics dictates a steady rebuilding strategy, seat by seat, vote by vote. The May elections represented the beginning of that: the Liberal Democrats made an impressive recovery from a low base, albeit with big strides to make in much of the country. That is the foundation of a slow but sure recovery.

There is, however, another possible future. The unsettling but exciting possibility that the ferment under the surface of politics might lead to an upheaval. As a veteran of the SDP revolt, I am wary of the pitfalls. It is instructive to observe that the 30-odd new parties launched and registered during just the last year crashed ignominiously in the local elections. Yet the possibility that something big could happen remains.

I see three elements in a new kind of politics.

The first is to recognise the power of outward-looking movements rather than inward-looking parties. Momentum is a brilliantly successful example, whatever we might think of its politics. A better model still is the transformation of the Canadian Liberals from near-extinction to the majority party of government. Justin Trudeau was the result of a concerted effort to open up the Liberal Party to a wider support base through open primaries for the national leadership and MPs. This generated the energy to lift them from distant third to first.

A second step is to break down tribal taboos by working with other parties. That is happening over Brexit in parliament, with dissident Labour and Conservative figures joining us in the centre to defeat the government. On the ground, we have even seen limited co-operation on the ballot paper.

Following constructive support from the Greens for my parliamentary campaign to defeat the Conservatives in Twickenham, I encouraged my local party to experiment with an agreement between themselves and the Greens, based on a common set of values and policies. The shared campaigning and leaflets proved popular and helped both parties. The Lib Dems won a big majority on the council, and the Greens have their first local representation (four councillors). This approach may not work everywhere - the model is mainly relevant where we are challenging the Conservatives and depends on local initiative and national goodwill. But it is grown up politics.

The third element is the beef: the message, the vision. Centrist politicians were asleep at the wheel when the financial system crashed. The casualties looked elsewhere. But now we see in Trump the havoc created by right-wing populism. At home, the chaos of Ukip nationalism has been absorbed into the Conservative Party. On the other side, the revolutionary left has turned the Labour Party into a projector screen for its fantasies.

By contrast, the Lib Dems are fizzing with big ideas. In recent months we have proposed agenda-setting reforms on health (notably an earmarked tax for the NHS and social care), education (such as abolishing Ofsted), homelessness (including mandating end of life care for the terminally ill), and big tech (such as breaking up monopolies). In the coming weeks, I will set out radical plans to reform British capitalism and to increase housing supply.

Rebuilding a credible, optimistic political movement from the bits and pieces of liberal and social democratic parties and factions is no easy task. But it is underway.

Vince Cable is the leader of the Liberal Democrats