LONDON (AFP) - British Prime Minister Gordon Browns deputy warned Saturday that he would likely face a renewed threat to his leadership after surviving serious blows last week. Lord Peter Mandelson predicted that rebels would likely try to dislodge Brown at the governing Labour Partys annual conference in September. Brown endured the worst week of his rocky premiership after Labour suffered historic losses in the June 4 European and local elections which saw the resignation of 11 ministers amid calls for him to quit and savage critiques of his leadership. The turmoil left Browns authority seriously weakened, newspapers said, with rebels still convinced Brown will steer Labour to defeat in the next general election, which must be held by June 2010. Mandelson, Browns de facto deputy, told The Daily Telegraph newspaper: Theres a small group who keep coming back. They wont be reconciled to the prime ministers leadership. However, he said he would not lose any sleep over the threat posed by them. Branding the attempts to unseat Brown a small earthquake, not many dead, Mandelson hinted that Brown should show more leadership and lighten up his demeanour. Secondly, in listening to people and respecting official advice you receive. And thirdly, introducing a bit of humour and jollity to your work. You dont have to be too grey or serious the whole time. You can do your work and enjoy it at the same time and include people along the way. Meanwhile Foreign Secretary David Miliband indicated that he considered quitting in the wave of resignations which left Brown fighting for his job last week. Some commentators say that had Miliband reportedly behind a plot against Brown last year gone, Brown would have had to follow. Id made my decision on Thursday (June 4), Miliband told The Guardian newspaper. Sometimes you can make your decisions with great planning and calculation and sometimes you have to make them rather more quickly. I made my decision in good faith... we all have to live with our decisions. He added: I know what we stand for. I know what our instincts are, but the voters dont, while calling for a period of competent, effective, stable government. Opinion polls suggest Labour will be defeated by the main opposition Conservatives, led by David Cameron, in the next general election. The Brown governments popularity has been hit hard by a scandal over lawmakers claiming generous expenses from the public purse for the upkeep of their homes, which has dominated news headlines here for several weeks. One of the most prominent Brown critics in the Labour ranks, former interior minister Charles Clarke, warned that the prime ministers survival depends entirely on Gordon. If, for example, our poll ratings go up or we win these (forthcoming) by-elections, I think the issue will go away and he can be confident he leads us into the next election. Otherwise, the issue will still be there, he said.