An archive of UK websites will cover just 1 per cent of the total by next year unless the new rules are introduced, chief executive of the British Library Dame Lynne Brindley warned today.
She said that researchers were "limited" legally and so are struggling to keep up with swathes of online material.
The 2003 Legal Deposit Library Act paved the way for the information to be preserved, but libraries said the law needs to be enacted through new regulations.
Currently, websites cannot be archived without permission and the average lifespan of a site is from 44 to 75 days, with one in 10 being lost or replaced each six months.
Dame Lynne's comments came as the UK Web Archive was officially launched today after six years of work.
She said: "Since 2004 the British Library has led the UK Web Archive in its mission to archive a record of the major cultural and social issues being discussed online. Throughout the project the Library has worked directly with copyright holders to capture and preserve over 6,000 carefully selected websites, helping to avoid the creation of a 'digital black hole' in the nation's memory.
"Limited by the existing legal position, at the current rate it will be feasible to collect just 1 per cent of all free UK websites by 2011."
The National Library of Wales and the Wellcome Library were also involved in setting up the archive, which aims to preserve records of websites for future research, for example those of MPs who will be retiring at the next general election.
Websites already included cover high street shops that fell prey to the recession such as Woolworths and artist Antony Gormley's project which saw thousands of people take to the fourth plinth in Trafalgar Square.
Minister for Culture and Tourism Margaret Hodge said: "The British Library's UK Web Archive is a fascinating snapshot of the way this country uses the internet. In the years since the internet began to be a part of our lives, the amount of information we have been able to access is simply unparalleled. The range of subjects is enormous, and reflects the diverse society we live in today."Reuse content