Young art historians are struggling to spot subtle but crucial differences between paintings by masters with similar styles because of the gradual demise of connoisseurship in academic art history, according to a leading expert in the field.

Universities are no longer training historians to tell their William Hogarth from their Francis Hayman, says Brian Allen, former director of the Paul Mellon Centre for Studies in British Art, and a trustee of the National Portrait Gallery. Instead students are being asked to focus on the social history of art.

“There are increasingly few younger art historians who are comfortable at being asked to make attributional statements,” he says. “Rather than studying Canaletto, a student is more likely to focus on some aspect of the sociology of view painting in 18th-century Europe.”

Allen says he is increasingly alarmed by young art historians who look “perplexed” if faced with a questionable picture. “It’s an area they haven’t really been schooled to do. There’s an element of fear.”

While social history is interesting, he says, it is only through recognising “the tiniest stylistic quirks” that historians can differentiate between, for example, certain paintings by Canaletto and his nephew and assistant Bellotto, which can look very similar. “One of the ways you can tell the difference is that Bellotto paints dogs in a completely different way. All these things seem pedantic – but it [connoisseurship] is pedantry in a way.”

One of the consequences of art historians being unable to distinguish between the hand of a master, an assistant or a copyist is that forgeries will be missed, says Allen.

He now fears that other subject areas “will fall into obscurity”. “If you look at the number of doctoral theses being produced in pre-20th-century art, it’s diminishing very rapidly. People are opting to do what you might call easier subject areas. If you’re writing about contemporary art, you don’t really need a body of knowledge to the same extent.”

Now, Allen claims, some of the best scholars coming through in the field of British art are from Italy, where, he says, they have a much more conventional classical education: “They’re better equipped to deal with the rigours of older art where you have to know languages, classical mythology, Greek and Roman history,” he says. “So many of our [art history] students these days have got almost none of those fundamental skills. It’s simply the way education has changed.”

The change to art history education started to happen in the early 1980s when the traditional focus on scrutinising paintings started to be replaced by a social history of the subject. “This has taken a kind of stranglehold on the way the history of art is taught,” says Allen. “Its exponents simply believe that connoisseurship and that kind of monographic art history has its limitations.”

The demise in connoisseurship has long concerned Allen – 25 years ago, he says, he warned that soon there would be no connoisseurs in the history of British art left. Now, he thinks this has almost come true. “There’s hardly anybody left,” he says.

His alarm extends beyond education to public collections. In a stinging rebuke to one of the country’s most prominent art institutions, the Tate, Allen believes it no longer has any “real experts” on British art. He is referring to the gallery’s decision in 2012 to lose Ian Warrell, a world authority on Turner, Anne Lyles, an expert on Constable, and Karen Hearn, a specialist in 17th-century art.

Responding to his criticisms, a Tate spokeswoman said: “Tate’s curatorial team comprises highly respected world experts specialising in British art from 1500 to the present day. Their scholarship and expertise is central to our exhibitions and displays programme, and integral to developing and understanding the collection. Rigorous research underpins all our activities at Tate.”

Allen will deliver his full condemnation of what he sees as the demise of traditional art history at a conference on Art, Law and Crises of Connoisseurship that will take place on 1 December and has been put together by ArtWatch UK, the art world watchdog, the London School of Economics and the Centre for Art Law (US).

Michael Daley, director of ArtWatch UK, says the idea of the conference grew from a realisation by various sectors of the art world that scholars were “falling down” on the job of monitoring restorations and of correctly identifying important artists.

“Art historians are not confident about art any more,” he says. “Nobody’s against social history. It is interesting, but if you read the literature now on Renoir, it’s all about frocks and society.”

The painting on the left is of the Ducal Palace in Venice by Canaletto. The one on the right is of a similar Venetian view by his nephew and assistant Bernardo Bellotto