The slow-motion disintegration of the Conservative and Labour parties is the key political fact of 2019. Brexit is the immediate detonator, but the underlying causes run deeper and create the opportunity to reshape politics.

Both of the large parties prospered because they were coalitions; they found space for liberals who argued for economic and social progress based on respect for individuals and communities, and for Britain’s role in the community of nations.

However, this approach has broken down. Although many social democrats and liberal Conservatives still instinctively prefer to argue their case within the larger parties, there are several reasons why this approach no longer works.

First, there is no time. The traditional parties are both committed to carrying through different versions of Brexit, but