President Nicolas Sarkozy could face the greatest challenge of his presidency in the next few days as a month-old protest against pension reform swells towards outright confrontation.

More than 3 million demonstrators - one in 20 of all French people - marched yesterday against the President's plans to raise the standard retirement age from 60 to 62. Tens of thousands of students joined the marches for the first time, threatening to radicalise the protests and broaden them into a rebellion against a deeply unpopular presidency.

Militant union branches in the railway and oil-refining industries were pushing last night for a showdown with Mr Sarkozy, who has made reform of the loss-making state pension system the make-or-break issue of his final 20 months in office.