The Government was on a collision course with millions of public sector workers today after union leaders warned of a series of potentially crippling strikes over pensions.

Leaders of 13 unions representing more than three million workers in the NHS, local government, civil service, fire service and other public sectors pledged to campaign together against controversial proposals to extend the pension age from 60 to 65.

Dave Prentis, leader of Unison, issued a blunt warning that workers will take strike action to defend their pensions.

He told the TUC Congress in Brighton that ministers had underestimated the anger of workers and did not understand their ''outrage'' which had been fuelled by big pensions rises for politicians and company directors.

''To those who think that the anger has subsided I say think again. I promise you this, we are stronger and more united than ever before and we will take strike action to defend our pensions.''

Trade and Industry Secretary Alan Johnson, who listened to a string of attacks from speakers over the Government's plans, told delegates he was confident that negotiation, which will resume next week, will resolve the dispute.