British Telecommunications has for 14 years owned a US patent to one of the key building blocks of the world wide web, it emerged on Monday.

BT is understood to own a US patent covering "hyperlinks", which allow users of the web to move between pages by clicking on pictures or text. But BT, which has frequently been criticised for responding slowly to internet opportiunities, has until recently made no attempt to exploit the patent commercially.

The patent, which expires in 2006, remained buried among 15,000 other global patents owned by BT until a "few years ago", when it was rediscovered in a routine trawl of BT's intellectual property.

The company has now decided to attempt to commercialise the invention, which analysts believe could be worth hundreds of millions of pounds. BT has yet to prove that it can defend the patents in court.

In the last few weeks BT has sent letters to internet service providers in the US regarding the patent. It has also engaged QED, a company owned which specialises in winning revenues for companies from unused patents they own, and which is owned by UK technology group Scipher.

BT said on Monday: "We are not trying to stop anybody using the internet, we simply want some reasonable royalties based on the revenues other organisations are enjoying from using this intellectual property.

"We are not trying to take anything away from Tim Berners-Lee" - regarded as the inventor of the world wide web - "but [BT] did invent a way of structuring information to make it easily accessible."

The company said it was a big operation to follow up the patent, which was why it had not looked to commercialise it until two years after the patent resurfaced.

"It is not something you want to shoot from the hip on," the company said.

Observers said BT was likely to face stiff opposition for trying to enforce a patent covering such a basic and important part of the internet.

However, it would not be the first company which has looked to enforce patents for internet-related functions.

BT's invention is understood to have emerged in the 1970s from research at the Post Office which culminated in a system called Prestel.

It allowed users to send messages and access screen-based information from third party servers, but lacked mass market appeal because it emerged in the era before cheap personal computers.

Patents were sought in 1976 and have already expired in countries outside the US. But the US patent was not granted until 1986, and still has six years to run.