David Cameron has played with fire over EU immigration - will he now get burned?

Of course, the PM isn't doing this so he can be humiliated over a retreat on a key policy. He's having to negotiate because he's been warned that the four-year ban could be illegal (because EU law bans discriminatory practices).

A brief bit of political history is helpful here. As the Centre for European Reform's John Springford has pointed out, the four-year idea first cropped up in Cameron's immigration speech in November 2014. At the time, there was a real panic on about the rise of Ukip and Cameron needed a long ladder to get him out of his hole.