Labour conference: Victory is a tall order, says David Miliband He said his brother and Ed Balls were right to acknowledge that fiscal responsibility "is not a choice" but a "requirement to be a party of government." However, the relationship between the two brothers is said still to be strained, two years after the divisive leadership election. The former foreign secretary remains popular among Blairites in the party but has so far resisted calls to return to the front bench. Two of David Miliband's biggest backers, the New Labour architects Lord Mandelson and Alastair Campbell, issued their own warning to the party not to retreat to its "comfort zone." Mr Campbell, the former spin doctor to Tony Blair who remains in regular contact with Ed Miliband, warned that the party was in danger of "complacency." "Don't be positive and upbeat because we're 10 points ahead in the polls," Mr Campbell said. We should be positive and upbeat if we are 20 points ahead in the polls with a month to go to the election. Mr Campbell said Ed Miliband must now develop policies that engaged the public. "It is up to the Labour Party, Ed in particular, to show that there's an understanding of the modern world, there's a policy agenda," he said. Lord Mandelson told delegates to be vigilant against the "attraction" of its "comfort zones and of complacency." He said Gordon Brown lost the last election because he did not look like a "natural PM" and drifted away from New Labour. Jim Murphy, the shadow defence secretary, called for a referendum on Britain's membership of the European Union, saying "almost everyone" in the Labour Party would campaign for Britain to stay in the EU. He told BBC Two's Daily Politics programme: "At some point, there will have to be a referendum ...