Some consumers living in urban areas are still putting up with "very low" broadband speeds, with disadvantaged areas suffering the slowest services, according to Ofcom.
Superfast broadband coverage varies widely between major urban areas, with Londonderry in Northern Ireland the best-performing city for availability at 99%, the regulator found.
The study examined 11 UK cities and found wide variations in the proportion of premises on a relatively slow broadband connection of 2 Mbit/s and below.
Consumers in Cardiff and Inverness were twice as likely to be on a slower connection than those in London or Birmingham.
Coverage of faster "next-generation" networks also varied between the cities, though in most it is now around 90%, according to the report.
While almost everyone in Northern Ireland's largest cities had access to superfast broadband, in Glasgow one in three people did not.
Ofcom said the findings were not consistent across all of the cities in the study, with many factors influencing the take-up and coverage of faster broadband such as the cost of deployment, the quality of historic infrastructure and local planning rules.
The proportion of premises on a relatively slow broadband connection tended to be higher in areas with lower incomes.
In Belfast, although almost all parts of the city had access to superfast broadband, around 5.9% of connections in the poorest areas were below 2 Mbit/s, but this fell to just 2.2% in areas with the highest incomes.
Ofcom said the results suggested that, in many cases, low incomes may be a barrier to customers choosing services with higher speeds.
The study also found superfast broadband was less widely available in those parts of the cities with low income.
In the most income-deprived areas of Manchester, superfast broadband availability was 80.6%, compared with 86% across the entire city.
The difference was more marked in Glasgow, where 57.8% of premises in the lowest income area had access to superfast broadband, which was lower than the city average of 67%.
Ofcom's consumer group director Claudio Pollack said: "Access to fast broadband is an important part of modern life, and a source of economic growth and investment across the UK.
"We know from previous research that rural areas often lack fast broadband coverage, something the Government is helping to address with public funding.
"Today's findings suggest that the usage and availability of faster broadband also vary widely between cities. We will carry out further work in this area to help bring faster broadband to UK homes,
whether in cities or rural areas."
Dominic Baliszewki, telecoms spokesman at broadbandchoices.co.uk, said: "Broadband is an essential utility nowadays and no one should be left behind on a connection of just a few Mbps.
"The plight of rural broadband customers is well documented but to hear of urban households putting up with slow speeds, particularly in disadvantaged areas, is extremely disappointing.
"At a global level, providing superfast broadband infrastructure is known to directly contribute to a nation's economic success, therefore it is crucial that everyone has access at an individual level.
"Broadband access is needed for everything from studying, socialising, financial management and even searching for a job, so if low-income households are also at a digital disadvantage, this can compound the problem even further."