One day in the summer of 1952, a group of villagers from Moniaive in Dumfries and Galloway set out on a day trip to the east coast in four streamer-bedecked buses.

The party travelled by way of Penpont, Crawford, Abington and Coulter, then stopped in Biggar for a cooling ice cream. The eventual destination was the Forth Rail Bridge. Well, it's what people did for fun back then.

Joining the trip was one Bill Richardson. He owned a photographic shop in Moniaive and also shot 16mm moving film using the moniker Richardson's Roving Camera. Adding a title card, he would later turn his footage into a 10 minute colour home movie called Children's Excursion.

Sixty-three years on, Richardson's documentation of that day is just one of the many films to have been digitised by the British Film Institute (BFI) as part of its Britain On Film project, a collaboration with UK partner organisations such as the Scottish Screen Archive.

The plan is to have made 10,000 similar films available to view online for free by 2017. The first batch, Children's Excursion among them, goes up this month. People will be able to search by subject or location using an interactive map, and in time add comments, provide further information and in some cases download material for use in anything from school projects to video art works.

As creative director of an organisation responsible for TV hits like The Lost World Of Mitchell And Kenyon, a collection of century-old documentary footage screened on BBC One to great acclaim in 2005, the BFI's Heather Stewart is well aware of the general appeal of this sort of material. But she had never before had first-hand experience of its emotional power and the deep personal connections it can hold until she watched Bill Richardson's 1952 film. What the 59-year-old Scot saw three minutes and 10 seconds into it took her breath away.

"My mother, a woman called Mrs Maxwell, my great-granny and my cousin Violet all walk in a row towards the camera followed by my granny," she says. "I almost fell off my chair ... I grew up in a family that didn't have a cine camera and I grew up without any moving images of my family so just to see that was absolutely fantastic."

It comes in the Biggar ice cream scene, and there's another clip of Stewart's mother later when the party reaches the Forth. She comes into frame wearing a striped cardigan.

"I felt a bit tearful," Stewart says as she recalls those filmic encounters with a woman who, three years later, would become her mother. "My daughter was 12 when my mother died and she didn't want to watch it. For me, my great granny died 47 years ago so that didn't touch me in that way. But seeing my mum, who died not that long ago, did."

There were other resonances too, she says.

"My daughter looks very like my mother and when I showed the film to some colleagues who knew my daughter, they knew immediately which one was my mother. So that was quite touching as well. Things survive, you know?"

Some things do, others don't. But that, too, is part of the appeal of the BFI's massive cache of home movies, newsreels and documentary footage. And here again, Stewart has a personal connection.

"When I was a kid, Moniaive was a thriving village with two lively pubs and five or six shops and a school and all of that," she says. "It's definitely not that now. I hardly go home because the family home has gone and most of the people I know are dead. When I go into the graveyard I know everybody, but when I go into the real village, when I go into the pub, I'm a stranger. But in this film I know pretty much everybody."

They're brief moments, to be sure, but those fleeting images in Children's Excursion are enough for Stewart to become a part of the national conversation she and the BFI are hoping to start by making this sort of footage widely available. She has also been able to add vital local knowledge to that particular film. It didn't say "Shot by Richardson's Roving Camera" on the tin - that was information she has been able to add.

"I only know it because I come from Moniaive not because I work at the BFI," she says. "There will be millions of people out there who know things like that and we'd like to be able to interact with that knowledge and make the data really rich".

Among the other films being released in this first wave are a Gaumont newsreel from the 1927 Up Helly Aa Viking festival in Lerwick; The Skimsters, which shows a waterskiing competition on Loch Earn in 1959; footage of the Galashiels Gathering of 1951; and, from 1938, Salmon Fishing In Skye, which pretty much does what it says on the tin until the point at which the Hebridean fisherman catch a shark in their nets.

Glasgow features in two films from 1963 titled Glasgow Trams - we see the familiar old trams in their green and gold livery - and in 1980's Great Western Road, a real-time trip down that street which shows people and businesses long gone, as well as a few that remain.

Other films, like Mark Littlewood's 1966 portrait of Edinburgh, are more experimental and impressionistic. Accompanied by a (slightly cheesy) orchestral score, Littlewood's camera travels the docks at Leith and Granton - we see hard-bitten trawlermen loading fish and ice into crates - then delves into the city proper, rising and moving in a series of tracking and crane shots which showcase the capital's stark architectural grandeur. In one extraordinary scene, Littlewood's camera captures in silhouette the memorial statue to the Royal Scots Greys on Princes Street, making the mounted soldier appear to glide across the screen with Edinburgh castle as the forbidding backdrop.

Although a massive project, scanning the 10,000 films digitally is relatively fast. What takes time and money is repairing the celluloid. Every can has to be opened and its contents examined, then a decision made about its quality, its relative importance and how quickly it should be made available online. The oldest film in the collection is from 1895 and there are many from the late Victorian and Edwardian era, so the BFI is digitising everything shot before world war one.

Those earliest films are all in black and white but from the 1950s onwards, when 16mm cameras became more affordable for ordinary families, many are in colour. "Colour is very important to people, it's very immediate, so for me the 1950s and 1960s are a great moment when colour starts to come in," says Stewart.

There's little doubt that Britain On Film will be a hit. As well as the success of The Lost World Of Mitchell And Kenyon, the BFI has collaborated with the BBC on an equally well-received series showcasing the pioneering 1920s work of Claude Friese-Greene, who pioneered the use of colour techniques from the 1920s onwards and made around 60 films between then and his death in 1943. The BFI also regularly releases DVDs of curated documentary footage. Films about transport and industry are perennial favourites among enthusiasts. One such release is Tales From The Shipyard, which featured a 1967 essay-film called The Bowler And The Bunnet in which Sean Connery opines on the state of worker-management relations in the Glasgow dockyards.

BBC Scotland, meanwhile, has produced programmes using documentary footage and last year collaborated on a feature-length film, From Scotland With Love, with a soundtrack by Fife-based alt-folk troubadour Kenny Anderson, who records as King Creosote. Again, it proved popular with audiences.

"There seems to be a burgeoning interest in looking back and at people understanding themselves and who are they are where they come from, as you can see from genealogy programmes on the telly," says Stewart. "And I know that once you get older, the more fascinating those things become."

It's that fascination which underpins the Britain On Film project and which has driven the BFI to undertake it. Never before has so much archive material been made available in one place, never before has the BFI been able to work with its partner organisations in Britain's nations and regions to present what Stewart calls "one message" to the public.

"Here, with one big go, we can all shout together and try to make people understand that there's something there, it belongs to them and they can go and enjoy it," she says.

And not only do we own this vast film heritage, we also star in it. Not us specifically, but people like us or related to us: our mums, our dads, our grand-parents. Perhaps even our Auntie Violets.

The first films in the ongoing Britain On Film project are available to view online now at www.bfi.org.uk/player