On Thursday, a by-election in a Southern Manchester constituency, Gorton and Denton, is shaping up to be a seismic litmus test for British politics.

After the previous MP, Labour's Andrew Gwynne, stepped down in January, an opening for a new MP has set in motion a battle between Labour and their insurgent challengers, Reform and the Green Party.

Oli Dugmore is joined by our senior data journalist Ben Walker to discuss.