ONE day in 1920, a large biplane passed low over the Railway Works and a man leaned bravely out with an unwieldy camera whose ‘film’ was a glass plate about five inches square.

What he couldn’t have known was that the images he shot would eventually be preserved with thousands of others in one of the buildings below, and made available to the whole world.

And if you’d told him those images would one day be shown on a big television at Wharf Green, he’d have said: “What’s a television?”

On Saturday, the second day of Swindon Film Festival, the festival organisers are teaming up with English Heritage at the Big Screen for Chocks Away! Take Off With Britain From Above. Vintage aerial views will be shown free to all who wish to see them. Britain From Above is a project that’s been running at English Heritage’s Railway Works headquarters since funding was secured in 2010, and is due to finish next year.

The 13-strong team of conservers, repairers, digitisers and cataloguers is headed by Verity Hancock.

She said: “It’s a project to preserve a unique and significant aerial photography collection which was taken by a company called Aerofilms Ltd, which started in 1919.

“It was set up by two men after the First World War – Francis Lewis Wills and Claude Grahame-White. They decided that with rapid technological advances they could set up a business and make money on a commission basis and also with postcards.

“They started the company flying borrowed planes from Hendon.”

Many clients were companies wanting views of their premises. Uses for these included simple display, proof of site size for tax breaks, and gifts for clients. There was also plenty of money to be made in providing aerial views for the public. Aviation was out of reach to most people until at least the 1960s, so a shot of their own home or town from above was a desirable novelty.

The most comprehensive set of aerial photos of Swindon and the surrounding area is the Adver’s, taken for various supplements over the years. However, the ones on the Britain from Above database are almost cetainly the earliest of their kind, and show a Swindon where the the railway was still king and challengers non-existent.

The Second World War saw Wills and Graham-White helping Operation Crossbow, taking detailed shots of German V-weapon installations on the Continent to assist Allied bomb-aimers.

The company went through various owners before selling its archive of historic images to English Heritage in 2007.

Britain from Above is making 95,000 of the oldest images, dating from 1919 to 1953, available to the public. Before coming to English Heritage they been stored in sheds and even toilet blocks in various locations across the country.

The conservators are led by Rosalind Bos. Their work involves skill, patience, nerve and frequent use of very soft squirrel hair brushes. Also, if they happen to spot a visitor’s nose wrinkling in their small lab, the conservators are quick to point out: “It’s not us.” Early film negatives can give off powerful odours of vinegar and cheese like those we sometimes associate with a laissez-faire attitude to personal hygiene.

As if that weren’t amusing enough, they can also blow up in the hands of the unskilled. “Our first step when we get a box,” said Rosalind, “is to start treatment in a fume cupboard. The gases they sometimes give off can be a health hazard.

“Nitrates can also self-combust at about 40 degrees, so they have to be kept away from sources of heat.”

Glass negatives, which were used until just after the Second World War, can suffer what the conservators call ‘glass disease’ with images sometimes peeling away from the glass beneath.

Later film negatives suffer their own problems, from gross chemical deterioration to curling up into something resembling one of Clint Eastwood’s cheroots in a Spaghetti Western. All are stabilised and preserved as much as possible.

Sometimes members of the team find themselves peering at things which truly startle them, such as preparations for the Queen’s Coronation or the aftermath of the 1952 Harrow and Wealdstone train disaster, in which 112 people died.

Once cleaned and preserved, the images are sent for scanning and digitisation by other specialists who use the latest technology to bring out as much detail as possible without altering the ‘truth’ of what the lens saw all those years ago.

Another team cross matches the images against maps and known information, allowing for easy searching of the tens of thousands of images already online.

“We’ve had over 10 million page views,” Verity said, “and over 25,000 people have registered. People can log in to use features of the website such as being able to zoom in on details.”

Saturday’s Big Screen showing runs from noon to 3pm, and the Britain from Above website is