Ofcom has revealed 1.4 million homes and offices in the UK are still unable to get broadband speeds of more than 10Mbps.
This means five per cent of premises are falling short of the speed specified in the government's Universal Service Obligation, which would ensure everyone in Britain has a legal right to request minimum speeds of 10Mbps by 2020.
Figures showed that the number of properties unable to get a decent broadband connection has actually fallen recently, as it stood at around 2.4 million last year.
But despite this improvement, Ofcom still believes there is a great deal more to do, particularly when it comes to improving the quality of service provided by telecoms firms.
Furthermore, the watchdog said about one in four properties in rural locations are still struggling with slow connections, as they are often situated some distance away from telephone exchanges and street cabinets.
Steve Unger, Ofcom Group Director, commented: "Mobile and broadband coverage continued to grow this year, but too many people and businesses are still struggling for a good service. We think that is unacceptable.
“So we’re challenging mobile operators to go beyond built-up areas, and provide coverage across the UK’s countryside and transport networks. Today we’ve also provided technical advice to support the government’s plans for universal, decent broadband."
Ofcom added that the speed required by the planned USO is sufficient to meet the current needs of a typical household.
However, it said households are likely to need greater speeds in the future, due to the emergence of new "data-hungry" applications.
The watchdog therefore plans to monitor the USO and recommend its minimum speed rises when it becomes necessary.