£5bn for full fibre - do the numbers add up?

Three months ago, Boris Johnson set a hugely ambitious target - giving every home in the UK full-fibre broadband by 2025. Now, at the Conservative Party conference, the Chancellor, Sajid Javid, has promised the funds to make that happen. 

Or has he?

In the press release previewing a speech promising as much as £50bn in new infrastructure spending, there is this section about broadband.

"We are setting out plans to invest £5bn to support the rollout of full-fibre, 5G and other gigabit-capable networks to the hardest-to-reach 20% of the country," it says.

"This doubles the previous commitment to support rollout to the hardest 10%."

Last year's Future Telecoms Infrastructure Review, commissioned by Theresa May's government, set an "ambitious target" of full fibre - a pure fibre-optic cable running directly into the building rather than to a roadside cabinet - reaching 15 million premises by 2025. 

The whole country - including about 30 million homes as well as millions more businesses and public buildings - would be covered by 2033, it added.