WHEN the Swedish Social Democrats unveiled a plan to force companies to hand over shares to its workers, opposition came from an unlikely source: ABBA. The pop group led a vociferous campaign against the proposal in 1982, hosting an open-air gig to raise funds to fight it and pledging to leave the country if it was implemented. ABBA won. Four decades on, Labour’s shadow chancellor John McDonnell is hoping for a better reception after taking a chance on the same idea.

Speaking at the Trades Union Congress on September 11th, Mr McDonnell launched his own version of the Swedish scheme, with large businesses compelled to give shares to worker-owned funds. This will bring slices of companies “into the collective ownership and control of the workforce” he declared.

Ownership of the means of production has been at the centre of the biggest changes in British politics over the past century, points out Mathew Lawrence of the IPPR, a left-wing think tank. Under Clement Attlee, nationalisation shifted ownership from private to state hands. Under Margaret Thatcher, it went the other way. Mr McDonnell wants to make as big an impact with a different method: collective ownership by the workers.

This idea lurks at the heart of Corbynomics and handing workers minority stakes in their firms is a small, but significant step towards it. That would help solve the problem identified by French economist Thomas Piketty, that returns on capital apparently outstrip growth in incomes, argues Joe Guinan, a left-wing thinker.

Not all are so keen. Under a Labour government, investors in Britain would face a triple whammy of Brexit, higher corporation tax and now the prospect of shareholder dilution. It is an unappetising mix. How it would apply to multinational companies is also unclear. Mr McDonnell insists that as long as Labour is straight about its plans, investors will not mind. Firms in which workers have a stake are more productive, according to many studies. The owners of Britain’s businesses may feel that there are other ways to improve the country’s lousy productivity.

As they stand, the proposals are more John Lewis than Karl Marx. The percentage companies must issue to workers each year is up for consultation, says Labour, as is the total stake the worker fund can control. But both are expected to be low single digits. Where Labour sets the limit—and whether it keeps it low—will dictate whether the scheme amounts to a tweak in favour of labour versus capital, or handing the means of production to workers. To Mr McDonnell’s supporters, the proposals are a modest shift; to his critics, they are the thin end of a thick socialist wedge.

How increased collective ownership would work needs clarifying. At present it has only a toehold in Britain. In total, co-ops account for roughly 2% of British GDP compared with about 7% in Italy and Germany. Britain also has no history of friendly industrial relations, which the new plans would probably require. Nor is there much enthusiasm among the workers. When Mr McDonnell announced the proposal at the TUC, he was met with a silence that contrasted sharply with the cheers for his plans to rollback Conservative anti-union legislation.

What will make the unions happier is Mr McDonnell’s fresh willingness to go beyond Labour’s last manifesto, which was stuffed with goodies for the middle classes such as scrapping university tuition fees. In front of an audience of trade unionists, Mr McDonnell said that his team was combing the manifesto see “whether or not it stands the test of time, whether or not it needs to be radicalised”. Labour is slowly heading further left. Unless someone follows ABBA’s lead and issues an SOS.