Ofcom has warned ISPs they need to do a better job of explaining broadband speeds.
The watchdog said that during a survey, 85 percent of mystery shoppers were given an estimated maximum speed by the ISP when enquiring about a broadband contract.
However, 42 percent had to ask for the speed, it was not voluntarily offered by the ISP.
Furthermore, 74 percent of mystery shoppers were not told the actual speed was likely to be less than the estimated maximum quoted.
Ofcom's research revealed that ISPs use different methods for calculating the maximum speed, leading to varying estimates from ISPs regarding speeds offered on the same line.
The watchdog also said some ISPs offer a speed estimate covering a wide range (such as 10 to 20Mbps) which can lead customers to expect a much higher speed than they actually receive.
As a result Ofcom says it will work with ISPs on tightening Voluntary Code of Practice on Broadband Speeds, in particular creating a universal speed measuring test, in a bid to ensure Brits are provided with more consistent and accurate information by Summer 2010.
The Code of Practice, which came into force in December 2008, has been signed by over 95 percent of UK ISPs.
Under the code, ISPs are required to provide consumers with information covering a number of areas before they sign a broadband contract.
The information includes the maximum speed that can be expected on a line and the factors that will affect their actual speed achieved.
"Consumers are now receiving more accurate information at the point of sale about their broadband service but our mystery shopping research reveals there is still significant further progress to be made, particularly in relation to the checkers used to calculate line speeds," said Ed Richards, chief executive of Ofcom.
"We will work with the internet service providers to ensure consumers receive the best quality information and amend the existing Code accordingly. We will continue to monitor and assess performance against the Code in the coming months."
Sebastien Lahtinen, co-founder of Thinkbroadband.com, said the research shows ISPs are failing to address the needs of today's consumers, who are not necessarily as technically literate as those buying broadband connections a few years ago.
"We were disappointed that Ofcom did not publish the results for each broadband provider, as we believe that consumers have a right to know how each broadband provider performed, as this may well indicate how open and transparent they are likely to be with regard to other problems," said Lahtinen.
Ofcom also said it had completed a second survey into broadband speeds and it plans to release the results in July this year.
The first survey took place in July last year and revealed that on average, broadband speed are 50 percent lower than advertised.