Tens of thousands of demonstrators are set to descend on Manchester as the Conservative Party conference opens in the city. Up to 30,000 protesters are expected to take part in the event, marching past the heavily guarded venue where Prime Minister David Cameron\'s Tory party is gathered. Organised by the Trades Union Congress (TUC), it has been billed as a march and rally for \"The Alternative - jobs, growth, justice\" in opposition to the coalition Government\'s cuts to public services and pensions. Activists taking part are believed to include direct action group UK Uncut and police are on alert for extremists attempting to hijack the peaceful union protest. They have promised a \"robust\" response to anyone causing trouble with a major operation under way to keep the peace. Assistant Chief Constable Ian Hopkins of Greater Manchester Police said: \"This event poses a number of security challenges to the city of Manchester, and we have had to put in place a significant policing operation to help meet these challenges. \"Organisers of the demonstration have been very open and co-operative with us and it is clear that their intention is to demonstrate peacefully, as is their democratic right. \"However, anyone wishing to usurp or upstage this event with any violent disorder will be swiftly and robustly dealt with by the police. \"We simply will not tolerate opportunistic criminality or disorder.\" A mass rally at the end of the march will be addressed by union bosses including Bob Crow, leader of the RMT, Mark Serwotka from the PCS union and Len McCluskey, general secretary of Unite.