It began as one of the Callaghan government’s new-fangled employment initiatives, a six-month Job Creation Scheme, but it over-ran somewhat - 25 years this month, to be precise - in the process creating a unique repository of Scottish film. Now, Scottish Screen Archive is about to show off some of the nation’s earliest screen offerings.

Celebrating its quarter-centenary with special screenings and a St Andrews night special on BBC2, the Scottish Screen Archive has not only revealed that there exist far more filmed images of Scottish life over the last century than we might imagine, but also that Scotland has played more of an instrumental part in cinema than most of us might think.

"Stop the average Scot in the street and ask how Scotland has contributed to the development of cinema, and you would hope that they would come up with John Grierson, father of the documentary, and of course Sean Connery and Ewan McGregor," says Janet McBain, curator of the Scottish Screen Archive. "But I suspect that not many people will suggest that Scotland had much of a contribution to make. One thing the archive has done is uncover Scotland’s long-neglected pioneering role in the development of the cinema."

McBain was one of three unsuspecting unemployed engaged through the job creation scheme to investigate old film stock accumulated by the Scottish Film Council, now Scottish Screen, and see if it might form the basis for some form of archive.

She had trained in strictly document-based archiving, although she had what she recalls as "a lay person’s interest" in films. "I remember thinking, this isn’t really a ‘proper’ archive job."

But, along with another of the original job creation trio, Annie Docherty, McBain has presided over the archive ever since. Tucked away amid the lofty terraces of West End Glasgow, her charges these days amount to some 20,000 reels of film, providing often astonishing insights into Scots inventiveness and imagination over more than a century.

Cultural icons, from Rob Roy to Harry Lauder, whisky to the Loch Ness monster, rub shoulders with monarchs and close-mouth weans, all of them slumbering in rack upon rack of cans, awaiting only the whirr of the projector to resuscitate them into the flickering celluloid life of a nation.

Among those featuring in the BBC2 documentary on Friday are two reels vying for the archive’s "oldest film" title: both are dated March 1896, one showing Queen Victoria pottering grainily around Balmoral, the other revealing the jerking bones of a frog’s leg, filmed by Scottish X-ray pioneer Dr John McIntyre.

Further eye-openingly early footage, taken by the enterprising Aberdeen bookseller and optical lanternist William Walker, shows the Gordon Highlanders marching off to the Boer War, while another reel - in more ways than one - captures a kitsch trio of prancing kilties in the country’s first movie advertisement, for Dewar’s whisky.

Other "firsts" include the first Scottish feature film, a 1911 version of my own ancestor Rob Roy, and the first Oscar-winning documentary - Seawards the Great Ships, made in 1960 - ironically, just as its subject was starting down the inexorable slipway into decline. The film opens with a spectacular "rudder’s eye view" of an ocean giant sliding into the Clyde: in the heat of the moment, the camera apparently went overboard but was later retrieved with no damage to the precious footage.

Heritage Lottery funding recently enabled a 13,000-can backlog to be dealt with. "For the first time we know everything we’ve got," says McBain.

Surprises still turn up, though. A recent acquisition was film shot in the 1890s by the Mitchell and Kenyon partnership for travelling "bioscope" showmen. It includes some of the earliest street scenes filmed in Scotland, as well as shots of Dundee jute workers which McBain describes as "absolutely superb - I thought I’d seen it all by now, but these are just . . . braw."