Up to three million UK households currently have a broadband internet connection below 2Mb, new research has shown.
The investigation was commissioned by the BBC and revealed that the problem is not just restricted to rural regions, but in the areas surrounding London.
By measuring the distances between properties and telephone exchanges, the study found that Basingstoke, a town in the commuter belt, and the county Hampshire were particularly badly affected.
Alex Salter, co-founder of broadband portal Samknows, told BBC News: "We had assumed that these notspots were in remote parts of the countryside.
"That may be where the most vocal campaigners are but there is a high incident of them in commuter belts."
He added that a slow connection could mean users were unable to use applications such as Facebook, Twitter or the BBC's iPlayer platform.
By 2012, the government is hoping that all homes in the UK will have access to broadband speeds of at least 2Mb as part of its Digital Britain project.