More than a million homes and businesses in the UK cannot get decent broadband, the communications regulator has reported.
Although coverage is improving, Ofcom found that 1.1 million – roughly 4% of properties in the UK – were stuck with speeds below 10 megabits per second.
The number has fallen from 1.6 million last year, Ofcom said in its Connected Nations 2017 report.
But it added: "In too many areas coverage is still poor, broadband speeds are slow, and mobile services are unreliable or not available."
This was particularly damaging for 230,000 small businesses which were not able to get a good connection to the internet.
For domestic internet users in rural areas the lack of coverage was significant, with 17% of homes not having access to good internet speeds – compared to just 2% of homes in urban areas.
Ofcom's chief technology officer, Steve Unger, said: "Broadband coverage is improving, but our findings show there's still urgent work required before people and businesses get the services they need.
"Everyone should have good access to the internet, wherever they live and work.
"So we are supporting plans for universal broadband, and promoting investment in full-fibre technology that can provide ultra-fast, reliable connections."
Ofcom is attempting to promote investment in full-fibre networks, although this is currently only available to 3% of homes.
The minister for digital, Matt Hancock MP, said: "We will have taken superfast broadband to 95% of the UK by the end of the year but we are not complacent and there is more work to be done.
"We are making sure that by 2020, every home and business in the UK will have access to reliable, high speed broadband.
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"There is also a clear need for rapid improvement on mobile coverage. We've recently removed outdated restrictions, giving mobile operators more freedom to improve their networks including hard-to-reach rural areas.
"But industry need to play their part too through continued investment and improvement in their networks, making sure that customers are not paying for services they don't receive."