Casual observers will be confused about the resignation of Iain Duncan Smith. His "Dear Dave" letter criticised not only the cuts in disability payments but the Chancellor’s austerity agenda as a whole, arguing that it is perceived to be serving a “political” rather than “national” interest.

“Hang on”, I hear you say,” Iain Duncan Smith? The Not Very Quiet Man? The man who has spent six years trying to deconstruct the welfare state? This Iain Duncan Smith is now agreeing with John McDonnell? Pull the other one, it’s got bells on.”