Homes and businesses will have a legal right to demand high-speed broadband by 2020, the government has said after rejecting a voluntary offer from BT.
Openreach, owned by BT and responsible for the infrastructure, offered to speed up improvements to 1.1 million homes.
The government has promised that the whole of the UK will have access to speeds of at least 10 Mbps by 2020.
BT said it respected the government’s decision.
The government believes the regulatory Universal Service Obligation offers “certainty”.
Under the plan, broadband providers will face a legal requirement to provide high-speed broadband to anyone requesting it, subject to a cost threshold.
Regulator Ofcom said that 4% of UK premises, or about 1.1 million, could not access broadband speeds of at least 10 Mbps.
It said poor connections were a particular concern for small businesses, with almost 230,000 unable to get a decent service in rural and urban blackspots.
Matt Hancock, minister of state for digital policy at the department for Digital, Culture, Media and Sport, said on the BBC’s Today programme: “Access means you can phone up somebody, ask for it and then someone has the legal duty to deliver on that promise.
“It is about having the right to demand it, so it will be an on-demand programme.
“So if you don’t go on the internet, aren’t interested, then you won’t phone up and demand this.”
In response to the announcement, BT said: “BT and Openreach want to get on with the job of making decent broadband available to everyone in the UK, so we’ll continue to explore the commercial options for bringing faster speeds to those parts of the country which are hardest to reach.”
Rival firms, which had talked of legal action if the government accepted BT’s offer, welcomed the decision.
Both TalkTalk and Sky said the government had made the right decision.
Tristia Harrison, TalkTalk chief executive, said: “By opting for formal regulation rather than weaker promises, ministers are guaranteeing consumers will get the minimum speeds they need at a price they can afford,” she said.
“The whole industry now needs to work together to ensure customers see the benefits as quickly as possible.”
Stephen van Rooyen, Sky’s UK and Ireland chief executive, said: “Government have made the right decision by choosing a fair and transparent approach that maintains competition, keeps prices fair and gives consumers a legal right to request broadband.”
Following the introduction of secondary legislation next year, it is thought it will take another two years before the right is enforced by Ofcom.
Under BT’s offer, which the company had said would cost up to £600m, 98.5% of premises would have had access to a fixed broadband service in 2020.
Another 0.7% would have access to a service delivered by a combination of fixed and wireless connections.
The remaining 0.8% in the most difficult-to-reach areas would have been guided toward satellite or on-demand fibre solutions.