The main reason why Nigel Farage is desperate for Ukip to win next month's European elections is that he believes victory for his party will force Labour to guarantee an EU referendum. As he said recently: "The way to get a referendum on Europe is to beat Labour in May and force Ed Miliband to promise a vote on Europe if he becomes Prime Minister. If both the big parties promise a referendum, we should get one. That's why all our concentration is on Labour in the next few weeks."
To date, Miliband has said that he would only hold a referendum in the event of a further transfer of powers to Brussels, a condition that he believes is unlikely to be met. The result is that the Tories are able to boast that the only way to guarantee an in/out vote on EU membership is to vote Conservative in 2015, an attack line that Farage recognises has the potential to do increasing damage to Ukip. Given the likelihood that Labour will be the largest party after the general election (not least thanks to the divided right), Farage needs Miliband to U-turn if he is to avoid losing EU withdrawalists to the Tories.
But when I asked a senior Labour source if there was any prospect of this, he told me: "The idea that Labour will change position is as unfeasible and ill-thought out as everything else Farage says." He pointed out that both the shadow cabinet and the PLP (with the exception of mavericks such as Kate Hoey) were "united" behind Miliband's stance and said a future Labour government would not allow itself to be "paralysed" by an arbitrary referendum. Instead, it would promote "the national interest" by only holding a vote in "the unlikely event of a further transfer of powers" and focusing on tackling the living standards crisis.
While Farage managed to force Cameron to promise a referendum against his wishes, there is no chance of him enjoying a similar success with Miliband. Unlike the PM, the Labour leader does not lurch, he does not U-turn. When a stance is adopted, typically in the form of a detailed speech, it is maintained. With Labour far more united than the Tories on Europe (a reversal of the situation in 1975), there is also no prospect of Miliband coming under comparable internal pressure to Cameron.
If Ukip do win the election, as the polls suggests is increasingly likely, the Labour leader will speak again about the need to restore trust in politics and to address the root causes of the party's support. What he will not do is promise an EU referendum that is neither in his interests nor those of the country.