A new code of practice from Ofcom comes into effect today that will mean broadband providers have to be truthful about the speeds they offer customers.
95% of the UK's ISPs have signed up to the voluntary code, which is being introduced by the regulator after research showed that customers don't always get the speeds they were promised.
Companies must now provide consumers, at the point of sale, an accurate idea of the maximum speeds their lines will see.
In addition, the new code also means providers have to explain exactly what "fair usage" means, a phrase often used to when the companies put limits on deals advertising as "unlimited downloads".
Companies signed up include AOL, O2, Orange, Sky, TalkTalk, Tiscali and Virgin Media.