Turner on the Web: Is this the future for access to museums' hidden masterpieces?

They have been hidden from view for 150 years, thousands of exquisite sketches and watercolours demonstrating the genius of one of Britain's greatest painters – Joseph Mallord William Turner.

About 30,000 works on paper, as well as the 350 canvas oil paintings for which Turner is famed, were bequeathed to the nation when he died aged 76 in 1851, the most generous gift of art ever given to Britain.

The sheer size of the bequest has been a problem. Many works were fragile, making general public access inadvisable, and there have been regular calls for parts of the collection – held by the Tate – to be sold off. Only a fraction has ever gone on permanent display.

But today the entire Turner bequest will be on view to anyone with an internet connection, thanks to a £1m investment by sponsors, the National Lottery and the Tate itself.

It means that millions of computer users can see how the artist regarded as the first Impressionist transformed the briefest of line drawings into masterpieces which reveal the force of nature – notably at sea - in dramatic depictions of light.

His annual tours through Scotland, Wales, the Midlands or the West Country can be retraced as he produced copious sketches, tested flashes of colour and made notes which became the private library of ideas for his great works.

By keying in place names, users can even see whether he sketched a town or county. Turner's foreign jaunts – to Switzerland, Germany, Italy and France – can be recreated.

Ian Warrell, the Tate curator who has overseen the laborious process of bringing every work of art out of storage, photographing it digitally and describing what is known about it, said that viewing the sketchbooks was "like looking over Turner's shoulder".

"If you visit a site he has visited, you can see he stalks his subject. He walks around it from several points of view, taking several ideas before he alights on one that he might put down in more detail. But it isn't always that one that he will develop in the studio. Sometimes it is the most fleeting sketches that become paintings. He had the most amazing memory and sometimes even the most rudimentary lines are all the information he stored away for bigger works."

The detailed work has even helped with the reattribution of 11,000 of the works, of which little was previously known. The first, and last, inventory of them, was carried out by AJ Finberg 93 years ago.

Eric Shanes, the author of eight volumes on Turner and the curator of the Royal Academy's exhibition last year, said the collection had to be "the most munificent bequest left to any nation by any artist".

"The sheer size has, of course, caused its own downfall," Mr Shanes said. "If it was only a small amount of work it would be very accessible, but the fact that there's so much of it means that public access has always proved problematic."

To be fair, members of the public could get a glimpse by appointment with the Tate's print room but few visitors did.

"This is a fantastic new stage in the relationship between Turner's great legacy to the nation and the British public. You can't just have the man on the Clapham omnibus rifling through delicate pages of sketchbooks. But now anybody with a computer can trawl through this material without endangering it."

Oliver Vicars-Harris, the new media consultant for the BT-sponsored project, said there were even advantages to seeing the works online. Enhancement meant viewers could often see details on screen that were almost invisible to the naked eye. It is also possible to search for specific areas of interest – pictures with sunsets, for example.

And as some of the original 300 sketch books were broken up into individual drawings in the last century, the digital technology also means they can be "reassembled", allowing them to be viewed on screen in the order in which they were originally made.

The project is part of a bigger scheme called Insight which aims to put the entire Tate collection online. Around 20,000 paintings and drawings have been included so far, but the addition of the Turner bequest today more than doubles at a stroke the number of works available to the general public.

The first tranche of work was funded with £500,000 from the Heritage Lottery Fund and a donation of £377,000 for the next stage has come from the Government's New Opportunities Fund, a lottery distributor which gives to educational projects. The Tate has also put in money of its own.

The scheme is an example of the revolution the internet is creating in the production, viewing and sale of art. Britart.com is among the enterprising dealers who have taken up selling art online. The BBC's new digital television channel, BBC4, will include an online art gallery of the best paintings in Britain when it launches tomorrow.

The project has even encouraged the Tate in a still more ambitious scheme. With the bulk of Turner's art held in London, the Tate believes it could create a complete catalogue of his oeuvre online by persuading the owners of the rest of his 2,700 works worldwide to take part.

Yet there were many times when it looked possible the Turner bequest would not survive intact.

The artist, who was born in London in 1775, the son of a barber, had stipulated in his will that a special gallery should be built for the purpose of housing his collection. It never materialised. For years, the bequest was held in seven tin trunks in the basement of the National Gallery before the completion of AJ Finberg's inventory.

The works on paper were then stored by the Tate until 1928, when a flood prompted their removal to the Prints and Drawings Room at the British Museum where visitors required a ticket for access.

Only in 1987 was the archive reunited at the Tate. Even then, access was restricted by the gallery's opening hours. From today, those restrictions have been banished.

"Now that the Insight project has brought the Turner bequest online, millions of people, worldwide, will be able to share in the enjoyment of these great works," Sandy Nairne, the Tate's director of programmes, said yesterday. "This is a great day for Turner."