The prospects of several other companies that compete with Openreach and have pledged billions in investment for their own initiatives would be thrown into doubt after the debut of a free government-run service.

“They all would disappear,” Mr. Howett said. “There is no way consumers are going to be paying them if they can get it for free from the government.”

How has the concept worked elsewhere?

The only comparable project is in Australia, where the National Broadband Network has tried to wire the country with fiber internet over the last decade. That project has been roundly criticized for delays, running over budget and not delivering the quality of service that was promised.

Governments elsewhere have taken different approaches. In South Korea and Japan, where more than 95 percent of the households and businesses have fiber broadband, the government played a crucial role, including helping companies secure loans to pay for the costs.

In Latvia and Portugal, other countries with high internet coverage, government grants have helped businesses pay for the buildup. In the United States, a fee on cellphone bills is used to pay for subsidies to businesses to expand broadband in rural areas, though it does not require fiber networks to be built.

“Lagging in fast internet is clearly a problem when the future of the global economy will depend much more on connectivity,” said Kevin Allison , who studies government tech policy with the Eurasia Group in Berlin.

Why is Britain lagging?

Britain has wide coverage for what was once the fastest internet technology, known as superfast. But it now lags far behind other leading economies in the next-generation networks. The new technology, based on fiber rather than copper cables, delivers information faster and more reliably than the aging systems. A high-definition movie can be downloaded in less than a minute.