Bandwidth-hungry services such as iPlayer are proving popular
One million UK consumers have exceeded or come close to exceeding their broadband usage limit, research from consumer group uSwitch has found.
So-called usage caps, where internet service providers limit the amount of bandwidth users can have in any given month, are standard practice.
But the majority of users are still confused by the bandwidth curbs imposed on them, the research found.
For some who go over their limit the penalty is disconnection.
"With so much reliance on broadband, having the service disconnected could feel to someone as serious as having their electricity cut off," said Tim Wolfenden, spokesman for uSwitch.
Its survey found that 56% of broadband providers who advertised services as "unlimited" did impose usage caps and were prepared to cut people off if they used their service to excess.
Only two out of the nine actually said what these limits were.
As a result, uSwitch found that 80% of UK broadband customers either wrongly thought that they had an unlimited broadband package or did not know what their limit was.
"Broadband companies should not be allowed to class their packages as unlimited if they are not," said Mr Wolfenden. "As providers aren't choosing to be fully transparent about this issue people need to be savvy when choosing their broadband and pay close attention to the small print."
6.2m customers thought they had no usage cap
7.5m did not know their download limit
One million have reached or nearly reached their limit
22% of broadband providers advertise the true limits of their packages
Net suppliers argue that such caps are necessary if they are to continue to offer a good service to all at the prices consumers have come to expect.
The Internet Service Providers' Association (ISP), which represents UK ISPs, has strict rules on how such caps are passed on.
"An ISPA Member must not deliberately operate bandwidth caps unless it makes available to its customers and users in a clear manner the nature of the caps that apply," said a spokesman for ISPA.
Fair usage policies are generally found in the terms and conditions of a broadband contract but, according to uSwitch research, only one in four people actually read it.
WHAT THE ISPS OFFER
Tiscali - advertised as unlimited, has fair usage policy but with unspecified excess, will cut off those deemed heavy users
Be - advertised as unlimited, unspecified excess, will not cut off users
Sky - unlimited with no usage barrier or cut off policy for those on its own network. 40GB monthly limit for other customers.
Virgin Media - unlimited but traffic of heavy users is shaped at busy times
Toucan - advertised as unlimited, with unspecified fair usage, will cut customers off
BT, advertised as unlimited, unspecified fair usage, will not cut users off
AOL, 40Gb limit, will remove users who exceed it
Plusnet, 30Gb peak-time limit. Those exceeding their limit will be encouraged to upgrade
Orange, advertised as unlimited, unspecified excess, will remove heavy users
Usage levels overall are still relatively low. Data published at the beginning of 2008 by broadband provider TalkTalk showed that half of its customers used less than 1GB (gigabyte) per month.
This is the equivalent of two standard movie downloads, 200 five minute music files or 225 minutes of TV from a service such as iPlayer.
As catch-up TV services such as the iPlayer get more popular, usage could explode, thinks Mr Wolfenden.
With an eye to this, Sky has recently launched an unlimited broadband package, Sky Max, while others, such as Be, allow for high usage patterns.
Freeing consumers from usage caps would come at a price, said Andrew Ferguson, editor of broadband news site ThinkBroadband.
"Without some form of usage control prices would be higher; £30 and upwards rather than free and upward we have now," he said.