Labour said its proposed overhaul of Britain’s telecoms infrastructure would be paid for by raising taxes on tech firms such as Alphabet’s Google, Amazon and Facebook and using its Green Transformation fund.

The addition of BT to Labour’s nationalisation plan sent the group’s shares down as much as 3.7 percent, wiping nearly half a billion pounds off its market value.

Analysts said that the share price reaction was relatively muted as investors do not expect Labour to win the 12 December election.

Labour said it would nationalise Openreach - the fixed-line network arm of the country’s biggest broadband and mobile phone provider - as well as parts of BT Technology, BT Enterprise and BT Consumer to create a “British Broadband” public service.

“It’s time to make the very fastest full-fibre broadband free to everybody, in every home in every corner of the country”, Labour leader Jeremy Corbyn said in a speech, according to an extract released by the party.

He will call the current network patchy and cast the plan as one that would “reduce people’s monthly bills, boost our economy and improve people’s quality of life”.

BT was the flagship of Margaret Thatcher’s privatisation policy when it was floated by her Conservative government in 1984.

The cost of nationalising parts of BT would be set by parliament and paid for by swapping shares for bonds, Labour said.

Matthew Fell, CBI’s Chief UK Policy Director, said: ‘Fast reliable broadband is an absolute priority for people and firms and does need improving. But Labour’s plan is not the way to do it. The roll-out of full-fibre broadband across the country is underway, and all renationalisation will achieve is to slow down a process that needs speeding up.

 “It is private sector investment that has driven connectivity, massively widened internet access and put faster speeds within reach for most UK households. This progress will be stopped in its tracks and the bill passed to pensioners and savers. With so many challenges facing the UK, blinkered ideologies must be left behind and replaced by forward-looking public-private partnerships that deliver rather than delay. As the scope of Labour’s radical renationalisation plans expands almost daily, firms around the world lose confidence in the UK as a place to invest safely. Some will be asking if they are next. This threat damages the livelihoods of communities across the country. It’s time for all parties to work with business, not against it.”