This would require a change of law, and is likely to be in the Liberal Democrat manifesto.
TUC general secretary Frances O’Grady welcomed the move, saying: “Denying unions access to modern voting technology is anti-democratic and ridiculously archaic in today’s online world.”
Cable told the Independent last week: “The Conservatives have an ideological aversion to trade unions and have repeatedly tried – and failed – during this parliament to curtail their mandate”.
A Tory party source said last night: “Our proposed reforms to the trade unions level the playing field and make sure the system works better for everyone. Sensible, pragmatic reforms that are good for our economy and fair for society.”