About three million homes in the UK have broadband speeds of less than two megabits per second (2Mbps) according to research commissioned by the BBC.
The government has promised to provide all homes in the UK with speeds of at least 2Mbps by 2012.
The research revealed that so-called notspots are not limited to rural communities, with many in suburban areas and even streets in major towns.
The government has pledged a range of technologies to fill the gaps.
"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 incidence of them in commuter belts," said Alex Salter, co-founder of broadband website SamKnows.
The SamKnows map offers an insight into where the homes are that the government needs to reach out to and connect to faster broadband.
It was created by comparing a sample of UK postcodes with a database of information about which providers offered services in the 5,500 telephone exchanges around the UK.
By working out how far properties were from a particular exchange, a picture of the speed of services can be determined as line length is a crucial factor in determining how fast broadband services will operate.
To get speeds of 2Mbps or more homes need to be 4km or less from an exchange.
Click on the left hand map for more details of the NotSpots around the UK and on the right for broadband speed results in the UK.
In Basingstoke, for example, 50% of telephone lines are more than 6km from the exchange, and in Hampshire as a whole a quarter of postcodes get less than 1Mbps.
For those struggling on slow connections it can mean a very different surfing experience from those enjoying higher speeds.
"In some cases people aren't able to shop online, aren't able to view certain websites or use social media applications such as Facebook and Twitter and they can't watch the BBC's iPlayer," said Mr Salter.
For commuters it could impact the way they work.
"It prevents flexible working. If the problem is fixed it means a lot more people could work from home which offers a very real way to improve society," said Mr Salter.
To date it has been difficult to get an exact picture of where notspots around the UK are or even how to define them.
Under 1% of homes in the UK cannot get any broadband at all.
Many official bodies around the globe define broadband as anything more than half a megabit per second.
But the Digital Britain interim report, which represents the government's strategy for broadband, raised the stakes by promising 2Mbps to all homes.
The Department for Business, Enterprise and Regulatory Reform, charged with delivering the Digital Britain report, has acknowledged that current definitions of broadband are "outmoded" in a world where some countries enjoy speeds of up to 100Mbps.
"Our view is that given the prevailing conditions and usage in the UK 2Mbps is right," said a Berr spokeswoman.
Ewhurst in Surrey is a prime example of a notspot. It is prime commuter belt but of the 1,000 or so properties only a handful can get speeds over 2Mbps.
Retired telecoms engineer Walter Willcox has been campaigning on behalf of residents for better broadband.
He has contacted both BT, which is planning to upgrade a percentage of its telephone cabinets with Fibre to the Cabinet (FTTC) technology and Virgin Media, which is upgrading its cable network.
Both have said extending their networks to Ewhurst would not be economically viable at the current time.
Lord Carter's Digital Britain report, due next month, will lay out the details of how it believes notspots can be eliminated.
Berr told the BBC it would be considering a range of technologies for communities such as Ewhurst.
"There are different ways of doing this which will vary from location to location. In some non-rural areas that are currently underserved the answer may be FTTC. Or it may be that the economics mean a wireless solution is the best option," said a Berr spokeswoman.
Broadband news site ThinkBroadband has launched its own NotSpot map, inviting people to enter their postcode if they think their broadband is slower than 2Mbps, as a means of launching grassroot campaigns to find solutions.
"Hopefully the map will show people that it is not just them suffering. If there are distinct clusters we can put people in touch with each other," he said.
People will be invited to comment on their speed which could reveal some easy solutions.
"There are some common problems such as the state of the wiring in a home or an old modem that are easily solved," said Mr Ferguson.
For others the solutions may be harder to come by.
He thinks the government could easily reach its target of getting 2Mbps broadband in every home by 2012.
"There are satellites up there which cover the whole UK and 3G could have been rolled out to more areas," he said.
But it will come down to a question of cost.
"Some places will be just too expensive to enable. If you say to someone you can have broadband if you pay £400 to have a satellite installed they might just say no thanks," he said.