David Cameron must make EU referendum promise more 'believable', Tory MPs urge Mr Baron said there would be "no downside in trying to pass this legislation," even if Labour and the Liberal Democrats try to block it. "If [legislation] were voted down, it would be abundantly clear which politicians are with the public in their wish for a referendum," he said. Mr Baron will not reveal the names of MPs who signed the letter but he did not approach members of the Government. The Prime Minister won round support from rebel eurosceptic MPs after he promised a referendum in the second half of the next parliament, if there is a Conservative government. However, the new letter is one of the first signs that the Eurosceptics in his party may not be satisfied. A Downing Street spokesman said there are "no plans to introduce legislation this side of the election rather than after the election." The letter comes amid reports that France and Germany have shunned Britain's efforts to review European powers ahead of a referendum. The Prime Minister ordered a series of reports on the influence of the EU earlier this year, as the first step towards negotiating a new relationship with Brussels. As part of this process, the Government also sent a survey to all 26 member countries asking for their opinions on the balance of power between the EU and national parliaments. According to the Financial Times, the French see the review as a product of British domestic politics. Countries including Italy and Sweden are thought to have taken part, but not the majority of nations.