David Cameron has ramped up his war on trade unionists by threatening a ban on London Underground strikes.

The threat on the opening day of the Conservative Party conference is likely to be the first of a series of attacks on workers' rights in Manchester this week.

Asked on BBC TV about putting legislation in place to prevent Tube strikes the Prime Minister said: "Seeing fewer strikes in our public services, that is something I would support.

"The Tube has been particularly difficult in recent years. Let's go through that process and set it out in our manifesto."

Mr Cameron is expected to follow yesterday's announcement with proposals to axe the publicly-funded £15.5 million Union Learning Fund, end free time off for union duties and insist strike ballots don't count unless at least 40 per cent of members vote.

His comments were met with fierce criticism by Underground workers' union RMT.

The union said any attempts to muzzle workers, a move long endorsed by London Mayor Boris Johnson and supported by many London Tory MPs, would be met by a sustained fightback.

RMT general secretary Bob Crow said: "Of course David Cameron wants to attack the most basic of human rights of ordinary working people.

"Throughout history hard-right governments of the rich, for the rich, have swung the axe at the unions."

He warned that "it will be Tube workers today and firefighters and nurses tomorrow.

"Any attack on RMT Tube members' rights will be met by an all-out campaign of industrial and political opposition."

Labour MP Jim Sheridan, the chair of the Unite parliamentary group, said Mr Cameron's obsessive victimisation of unions would not help the country.

Mr Sheridan said: "The Tories' perception of the trade unions as the enemy does not do business, workers or the economy any good.

"The coalition should be focusing on policies which actually help our workers and businesses thrive rather than pursue ideologically driven policies to strip the unions of their ability to stand up for workers.

"The Tories should realise that the unions are a positive force and stop pushing this them-and-us attitude between employers and the unions."