It will become harder for the PM to insist he can succeed when the europhile and the europhobe both declare he will fail.
Miliband doesn't want to make a pledge that raises more questions than it answers.
The Prime Minister can see the strategic as well as the economic logic that keeps Britain in Europe.
After withdrawing from the centre-right European People's Party grouping, Cameron has no right to tell his MEPs not to flirt with the anti-Euro Alternative für Deutschland.
A public vote offers the best prospect of responding to democratic alienation from the union, and establishing a secure platform for the UK's engagement in its future.
Shadow chancellor's comments suggest mood in the party is hardening against an in/out referendum.
Party sources tell the NS that they do not expect Labour to change its stance on a referendum before May 2015.
His party wants a eurosceptic but the PM may decide that he needs a business figure with a record of constructive engagement with Brussels.
Far from giving a voice to the people, the point of an EU referendum is to give a voice to a section of the Conservative Party.
Promising an in/out vote would shift the debate back onto Tory territory and could wreck a future Miliband premiership.