Dempsey's People: a folio of British street portraits 1824-1844 curated by Dr David Hansen, brings together 52 miniatures painted by the itinerant artist John Dempsey (1801-02-1877) over two decades. But these aren't paintings of aristocrats and gentry. They are portraits of street people: town criers, beggars, fruit sellers, and other everyday people with distinctive features and faces worn by hard lives who would be readily recognisable to many.

"He was not selling to the posh people," Hansen said.

His clientele was the emerging middle class who might not be able to afford to commission a large portrait from a major artist, but could pay for a miniature from a lesser-known one such as himself. The paintings of street people were his way of advertising his talents.

"He would go to a new town and depict their likenesses and stick them up in the pub where he was staying," Hansen said.

And this form of self-promotion worked: in one four-year period, Hansen said, judging by the numbers on his works, Dempsey was kept very busy: "He was painting on average three paintings a day, six days a week."

Hansen said that while Dempsey's technical skills in areas such as perspective were sometimes lacking, "his faces were extraordinary". The artist kept a record of many of the names, dates and locations of his subjects, providing valuable information for future researchers. They are, he said, the kind of people who would have been the ancestors of many contemporary Australian Anglo-Celtic citizens.

"Robert Bloomfield was the only one I had heard of when I started. He was a poet."

Bloomfield, born into a poor family, was a shoemaker whose best-known poem was The Farmer's Boy.

Hansen came across 51 of the works while working as senior curator at the Tasmanian Museum and Art Gallery two decades ago.

"They were in the drawer in the plan press marked U - Unknown and we had to move from one side of the building to the other."

His interest was piqued and even after leaving that institution he continued looking into the subject, eventually gaining a research grant and travelling to Britain to investigate Dempsey and his subjects. The result, after all these years and with the cooperation of his former employer, is the first public exhibition of the paintings.

The collection had been donated to the Tasmanian museum by Conrad Docker in the 1950s with the exception of one painting, Portrait of John Rutherford, depicting a man with facial tattoos, that he had given away. It is on loan to the exhibition from the Alexander Turnbull Library, Wellington, New Zealand.

Dempsey's People: a folio of British street portraits 1824-1844 is on display at the National Portrait Gallery until October 22. Tickets are available for purchase at portrait.gov.au.