It isn't clear exactly when Labour will release its manifesto, with party leaders trying to control the release of any details until they are formally unveiled.
It is the biggest new pledge of the campaign so far from Labour, with Corbyn comparing his proposed new British Broadband company to the establishment of the U.K.'s revered National Health Service.
There would be further costs associated with staff pensions, while Openreach now has a revenue of £5 billion a year.
"Remember, the BT group has over 100,000 people working every single day.
Well, I've got news for them - not anymore".
"The effect of the Brexit Party on United Kingdom politics has already been seismic and I am proud to have been among its candidates who, contrary to popular belief, are not a group of right wing, neo-nazis but a genuinely diverse bunch of largely ordinary, decent people who believe in our country, its history and the importance of our democratic system".
"How we do it is not straightforward, it needs funding, it's very big numbers, so you know we're talking £30 to £40 billion per building, and if you're giving it away it's again a sort of eight-year timeframe, it's sort of another £30 to £40 billion".
Unsurprisingly, the former state monopoly was unconvinced about the swing back into public-ownership.
Pushed on whether this means Labour would take these companies over, Mr McDonnell said: "I think we can come to an agreement - they're only 10% of the network and that's why we're doing this, because they've failed".
Microsoft Unleashes an Xbox Tsunami at X019
The full list of games announced can be found here, along with which games will be leaving the service by the end of November. Microsoft , however, wants customers to know it has learned its lessons from the Xbox One launch and won't repeat them again.
"So, shareholders are nursing massive losses on their investments should they have bought in at £5, say, two years ago - that's market forces".
Following Labour's announcement, shares in BT plummeted by almost 4 per cent and telecommunications group TalkTalk suspended the sale of one of its businesses.
James Lusher, Virgin Media's head of external communications, tweeted a gif of a raccoon stealing food from a cat bowl captioned with the words: "This mine now".
The roll-out of a full-fibre network would cost £20bn, ie adding an extra £15bn to the government's existing £5bn broadband strategy, he told the BBC, as a "one-off capital cost", with the cost of maintaining full-fibre "more than covered" by a tweak to corporation tax for multinationals such as Google and Facebook to pay more.
The roll-out would begin with communities that have the worst broadband access, including rural and remote communities and some inner city-areas, followed by towns and smaller centres, then by areas now well served by super-fast or ultra-fast broadband.
Launching the plan, Jeremy Corbyn, the Labour Party leader, said: "It's time to make the very fastest full-fiber broadband free to everybody, in every home in every corner of our country".
British Broadband would aim to cover between 14 and 18 million premises within five years and eventually achieve 92 per cent coverage.
Lobby group TechUK said the move was "fundamentally misguided" and would spell "disaster" for the telecoms industry and the fast-growing digital sector.
The announcement by Labour, which is now lagging Prime Minister Boris Johnson's Conservatives in opinion polls ahead of the December 12 election, sent BT's shares down as much as 3.7%, wiping almost half a billion pounds off its market value.