One of the mysteries of current UK politics is the absence of a credible voice of protest to the left of Labour in the way UKIP has found a vacant space to the right of Cameron Conservatives.

In last week's South Shields by-election UKIP won nearly 6,000 votes and came second to Labour while the Independent Socialist Party received 750. In the local elections UKIP gained 147 seats. The Greens, who oppose benefit cuts and might therefore be regarded as on the left, gained 22 seats.