Jeremy Corbyn has signalled he would lift the ban on “sympathy” strikes where workers show solidarity with other workplaces by taking industrial action in support.
The Labour leader told the BBC’s Andrew Marr Show he would seek to repeal Margaret Thatcher’s Employment Act 1980 that banned “secondary” strikes, restricting walk-outs to groups with a problem directly with their employer.
He said: “Sympathy action is legal in most other countries and I think it should be legal here.”
During the wide-ranging interview, Mr Corbyn also suggested Trident submarines could continue - but without carrying nuclear weapons.
And he appeared open to doing a deal with Argentina over the control of the Falklands - giving people living on the islands a say, but not a veto.
Jeremy Corbyn: "Nobody willingly goes on strike – it’s an ultimate weapon. Anyone who goes on strikes is making a sacrifice, they don’t get paid."
The comments on strikes were immediately seized upon by Tory ministers and MPs as evidence of the Labour leader wanting to return the country to the 1970s.
But some blamed interviewer Andrew Marr for attempting to pin down Mr Corbyn on industrial issues relevant decades ago. Former Labour deputy leader John Prescott claimed the interview was a "disgrace".
Asked directly whether he would commit to repealing the law on secondary strikes, he said: “Yes, of course. Nobody willingly goes on strike – it’s an ultimate weapon. Anyone who goes on strikes is making a sacrifice, they don’t get paid.”
But he was more anxious to discuss the “causes of people being upset, rather than the sympathy”.
He also expressed support for "flying pickets", which see workers travel to back the pickets of strikers in other places.
“Flying pickets are a term that was first used in 1972 I think or thereabouts and it was merely people moving around and showing support during a very difficult industrial dispute.
“We have to look at the question not of what trade unions are forced to do ultimately, but the causes of the problems in the first place.”
Hospital and ambulance staff take part in a march to the House of Commons during a 24 hour strike in protest at low pay within the National Health Service in 1979
“Sympathy strikes” were banned after the general strike in the 1920s but revived by Labour in the 1950s. It became an issue this week after Labour Shadow Chancellor John McDonnell, Mr Corbyn’s right-hand man, visited the junior doctors’ picket-line last week and said the party should "automatically come alongside our brothers and sisters in the trade unions and support them".
“Sympathy” strikes are restricted in the US and Australia, and the Tory government has introduced legislation to place more restrictions on trade unions.
Len McCluskey, the general secretary of the Unite union, welcomed Mr Corbyn's comments. "I think what I’ve seen this morning is a Labour leader on the side of ordinary working people," he told BBC 5Live's Pienaar's Politics.
The Labour leader was interviewed amid a review of Labour's defence policy, and against Mr Corbyn wanting to change party policy so it backs unilateral disarmament of nuclear weapons for the first time since the 1980s.
In the interview, Mr Corbyn, who has said he would never push the nuclear button even if he could, said the new Trident submarines "don’t have to have nuclear warheads on them".
The nuclear missile-carrying Trident submarines. The Government is likely to decide this year whether they should be renewed
On the Falklands, he said: "I think there has to be a discussion about how you can bring about some reasonable accommodation with Argentina.
"It seems to me ridiculous that in the 21st Century we’d be getting into some enormous conflict with Argentina about the islands just off it."
Asked whether islanders should ultimately have a veto, he said: "Veto, they’ve got a right to stay where they are. They’ve got a right to decide on their own future and that will be part of it. Let’s have that discussion and lets not set agendas in advance."