When Aaron Guy peered into a forgotten box in an ancient Newcastle building, he could not have guessed the treasures contained inside. The curious photo archivist had stumbled upon a remarkable set of original early glass negatives, detailing everyday street scenes of 19th-century Newcastle.

Meat markets, fairs, rag sellers, small corner shops and larger than life street characters are among the subjects which feature in the high-quality, 300-image collection.

Guy, who works at the city's Mining Institute, was helping to shift old furniture for the Society of Antiquaries when his attention was diverted to the box.

"The society were moving to a smaller building and were passing some of their belongings to other organisations," he said. "I was just being nosy really, peering into boxes, when I happened to spot that one contained some really old glass negatives. I thought they seemed interesting so we asked for permission to bring the plate boxes back to our office to have a proper look."

The work seems to date back at least to 1880 and the cohesion of the images suggests at least a third of them may have been created by a single photographer. His deliberate documentation of working-class life was unusual for the period, perhaps more in tune with the celebrated street photographers who followed in his footsteps almost a century later, in the 1960s and 70s.

The most arresting images are from the Newcastle streets, but the collection also contains work from other parts of the north-east, most recognisably Tynemouth and Lindisfarne.

By 1871 Newcastle industrialist Joseph Swan had devised a method of producing dry photographic plates, which meant there was no immediate need for a darkroom and chemical processing, and made photography more convenient and commercially viable. Within a few years his city factory was the largest and most successful manufacturer of dry plates in the world.

By the 1880s, Newcastle was prosperous and sophisticated. It had a thriving cultural and intellectual scene, with frequent lectures, debates and scientific demonstrations. Yet this photographer chose to point his lens at ordinary people.

"We know very little about where these negatives have come from," Guy said. "They were never catalogued and the society doesn't recall how or when it came by them. We aren't even completely sure whether they are one photographer's archive, or if they were produced by several individuals. Photography would have been a very expensive hobby at that time, but this person was shooting in a very contemporary way.

"Despite the cumbersome equipment he would have been using – a large plate camera, probably on a tripod – I would describe this as observational documentary, almost photojournalistic in style.

"The work doesn't look staged, but if it was then the photographer was doing things very differently from his contemporaries. This work feels less distant and more engaged than other series I have seen.

"It may have been someone with means, or a commercial photographer with quite a distinctive viewpoint, who decided that Joe Bloggs on the street was more interesting to photograph in his spare time than the high society of Newcastle. He was really quite ahead of his time in that respect."

Guy and his colleagues are still scanning the work and researching locations and possible identities of the photographer. They are also keen to find another 15 boxes of plates which were sent by the Society of Antiquaries to other places.

"I was really quite lucky to find this box," he said. "I don't know if someone forgot it or planned to pick it up later. The aim now is to date and catalogue the work, and then to put it out to other organisations in the city and hopefully get it seen, because it really belongs to the people of Newcastle."