Colin Gleadell reveals the conundrum at the center of the Canaletto market. The master had a nephew Bernardo Belloto who copied his works and

The differences are crucial because the phenomenon of 18th-century Venetian view paintings, sparked by the insatiable demand of English aristocrats doing the Grand Tour, is rife with uncertainties about authorship. “In the 19th century, ‘Canaletto’ was the standard description of all 18th-century Italian view paintings,” Beddington explains. “Even now, seven-figure sums are paid for dud Canalettos. Buyers should be extremely cautious.”

His interest in Venetian views began when he worked in Christie’s Old Master department from 1983-98, and his constant handling of them provided an experience second to none. “Canalettos were a frequent issue,” he recalls. “We were often faced with paintings accepted as Canalettos, but that were not so straightforward.”

The bible on Canaletto was, and still is, Professor W G Constable’s 1962 catalogue raisonné of some 500 works. But it became clear that there were changes to be made. Even though the work was revised after Constable’s death in 1976 by another scholar, Joseph Links, and a supplement was added, it needs rewriting says Beddington.

A turning point came when he was given Constable’s archive by Links shortly before he died in 1997. From the annotations it was clear that Constable had doubts about some Canalettos, and his manuscripts show he intended to attribute them to Bellotto. “It’s there on the page. He wrote ‘Bellotto’ and underlined it – then crossed it out. He was right, but he lost his nerve. I’ve been intrigued about what was going through his mind ever since.”

In Links’s final supplement to Constable, published in 1997, it was Beddington who changed several attributions to Bellotto. He now believes 50 paintings in Constable’s catalogue are by Bellotto.

Canaletto and His Rivals at the National Gallery – interview with curator (Telegraph)