MANCHESTER - The euro zone crisis is a threat to the global economy and Europe's policymakers must act urgently to fix its banks and deal with its debt, British Prime Minister David Cameron said on Sunday."The euro zone is a threat not just to itself but also a threat to the British economy, but a threat to the worldwide economy," Cameron told BBC television on the opening day of his ruling Conservative party's annual conference in Manchester."Action needs to be taken in the next coming weeks to strengthen Europe's banks, to build the defenses that the euro zone has, to deal with the problems of debt. They've got to do that now. They've got to get ahead of the markets now."Cameron also said he was not about to "tear up" Britain's own deficit reduction plans, despite signs that the UK economy is struggling to grow.