Councils have urged the government to “reaffirm its commitment” to a minimum broadband speed to stop thousands of homes and businesses falling into a “digital twilight zone”.
The Local Government Association called for a “timetable for action”, saying it was “paramount” to press on with extending broadband to all of the UK.
Ministerial changes after the Brexit vote must not delay work, it added.
The government insisted it was on track with its broadband coverage plans.
The promise to give every household a legal right to high-speed broadband was announced in the Queen’s Speech in May, as part of measures to make the UK a “world leader in the digital economy”.
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The government expects an initial minimum speed of at least 10 Mbps (megabits per second) by 2020 under the new “broadband universal service obligation” (USO).
The pledge is included in the Digital Economy Bill, which will also include powers to direct Ofcom to regularly review the speed provided to ensure it is “still sufficient for modern life”.
Council leaders said they supported the creation of a national minimum broadband speed, but called for a “safety net” for those who were unlikely to be covered by the plan.
The government plans to set a reasonable cost threshold above which the remotest properties could be expected to contribute to the cost of their connection.
Mark Hawthorne, from the Local Government Association (LGA), said good digital connectivity was “a vital element of everyday life”, and key to the economy.
A minimum speed was “a good start”, but it must keep pace with national average speeds, especially at peak times, he stressed.
“Without this there is the real possibility of some areas – particularly in rural and hard-to-reach areas – falling into a digital twilight zone.”
The LGA’s call comes a day after Ofcom announced proposals to make BT’s Openreach division a distinct and legally separate company from BT to ensure “faster, more reliable broadband.”
But Ofcom stopped short of calling for Openreach – which runs the UK’s broadband infrastructure – to be spilt off entirely.
Responding to the LGA’s intervention, Digital Minister Matt Hancock said nine out of 10 UK homes and businesses could already get superfast broadband, and Britain was on target to reach 95% coverage by the end of next year.
Fast and reliable broadband was “a must these days”, he added, saying the bill to make the minimum speed requirement law was currently going through Parliament.