Might the unthinkable happen, and the voters of mining and railway towns in West Yorkshire abandon more than a century of loyalty to Labour and vote for Boris Johnson?

The open-air market of Castleford presents an animated scene, until you look a little closer. Some of the Saturday stands are unused, and there are many fewer than when the town flourished in the heyday of coal mining. It’s not even lunchtime, and one stallholder is forlornly shouting “Two for a pound!” over his plastic bowls of satsumas, mushrooms and pineapples, scarcely the local diet. Inauspiciously, there is no Vote Labour stall, with banners and leaflets and hardy grandmothers extolling the virtues of the party’s candidate, Yvette Cooper, as I saw in previous elections.

Welcome to classic “Left Behind” country, a West Yorkshire community that has lost all its collieries and most of its glass, chemicals and textile industry, and whose people voted 69.7 per cent Leave in the EU referendum, in a constituency that has returned a Labour MP since time immemorial, if not before. But for how much longer? The long shadow of Brexit hangs over this constituency like a pall of pit soot. Here, Conservatives and Faragistes believe they can upend political history in Labour’s northern heartlands.