ISP NTL has received a barrage of calls from customers venting their frustration at its decision to limit broadband usage.

Users of its so-called 'unlimited, always-on' broadband service will now be restricted to downloading no more than 1GB of data per day, the company announced on Friday.

On its customer gripes website NTHellworld the company defines 1GB as roughly 100 large software programs, 200 music tracks, 650 short videos or 20,000 web pages.

The company insists only a few customers will be affected, but many people switched to broadband in the first place to make regular large music or video downloads faster and easier.

"If you occasionally exceed your data limit, this will not be a problem," states the company's MD, Azid Hussain on NTHellworld. "Our only objective is to limit very frequent or persistent heavy users that can impact other customers."

For the next 60 days NTL will monitor usage and alert those customers who exceed the limit. Only those that go over the limit three times within any consecutive 14-day period will be contacted, but the company says they will not be disconnected.

A poll on NTHellworld shows that 760 users will be switching to another service provider as a result of the caps and an anti-NTL website was set up on Friday encouraging users not to pay the hiked prices.

NTL says it no longer refers to its broadband services as 'unlimited', claiming it confuses customers. 'Unlimited' now means 'available at any time' rather than unrestricted usage. Sounds like a way of pushing users already paying high fees for the benefits of broadband toward even greater tariffs.

Many ISPs are making only small profits from broadband services and several leading ISPs in Europe have already offering 'tiered' systems, charging users for the amount of content that use, in order to make back some of the money invested in high-speed technologies.

BT Retail's 'no frills' broadband product, which provides basic internet connection without extras such as email services, also has a 1GB ceiling for downloads.