John McDonnell said that the plan would give staff a greater say over the direction of a company

Labour’s plans to give shares to workers would amount to a confiscation of shares worth £300 billion in 7,000 big companies, according to research.

Under a Labour government’s “inclusive ownership funds” every business with more than 250 workers would transfer 10 per cent of its shares to staff over a decade.

An analysis of official figures shows that the transfer would be worth between £270 billion and £300 billion, dwarfing the size of previous interventions designed to redistribute income.

Clifford Chance, a law firm which produced the research with the Financial Times, said that there was “no historic precedent” for such a large-scale state appropriation of wealth. Dan Neidle, a partner at the company, said that the plans would result in legal action from