The American who taught us to love home-grown art

There is some corner of Connecticut that is forever England. Opposite the Yale University Art Gallery in New Haven is the tastefully unobtrusive steel façade of the Yale Centre for British Art. Now celebrating its 30th birthday, it houses the largest collection of British art outside the UK – 2,000 paintings, 50,000 prints and drawings and 35,000 rare books and manuscripts, all amassed by one man – the philanthropist Paul Mellon.

A selection of the "greatest hits" from his collection – including paintings by Gainsborough, Constable and Turner, as well as William Blake's rarely seen illustrations for Jerusalem and William Caxton's edition of Chaucer's Canterbury Tales (the first book printed in England) – will arrive at the Royal Academy in London on 20 October.

The exhibition of 150 works is an encyclopaedic record of British art "from the birth of Hogarth to the death of Turner" and an intensely personal collection. There is much evidence of Mellon's gluttonous appetite for works depicting equestrian life, from a portrait of himself on horseback by Alfred Munnings to a fine collection by Stubbs. These include the first painting Mellon bought, Pumpkin With Stable Lad, the artist's anatomical drawings, and a delightful painting of a zebra looking bewildered against an English woodland backdrop.

As well as Turner's magnificent seascape Dort, not seen in Britain since 1966, there are Constable's rural landscapes and his cloud studies, inscribed on the back with the weather conditions at the time of painting. In portraiture, Mellon's preference was for small-scale domestic scenes, such as Gainsborough's rather stiff portrait of a provincial apothecary and his family, and the almost indecently intimate Mrs Abinton As Miss Prue in 'Love for Love' by William Congreve, by Joshua Reynolds, in which the actress is pictured in close-up, a faraway look in her grey eyes, her thumb thoughtfully in her mouth and a fluffy dog on her lap.

There is also Thomas Rowlandson's hilarious take on the Royal Academy's summer exhibition, The Exhibition Stare-Case, Somerset House, in which the visitors' queue becomes a comical version of Dante's descent into hell, with ladies tumbling down the steps and men ogling them.

Mellon's collection had its beginnings, as many of the best things in life do, with a lunch at Claridge's. He arranged to meet Basil Taylor, the librarian of the Royal College of Art, to talk about an exhibition at the Virginia Museum. It was 1959 and the London art market was struggling to escape from post-war doldrums. British art was overlooked, unloved and, crucially, inexpensive. "By the time we were drinking our coffee," Mellon wrote later, "it had been more or less agreed that I was going to collect British art and that Basil would be my adviser."

It was a natural progression for the middle-aged American and lifelong Anglophile, who was the only son of Andrew Mellon – the Pittsburgh banker who served as treasury secretary to three presidents and funded the building of the National Gallery of Art in Washington. Mellon junior, thanks to his English mother, was baptised in St George's Chapel at Windsor Castle and, following his parents' divorce, spent idyllic holidays by the Thames which laid the foundations for his love of the English landscape.

From 1959 onwards, Taylor kept Mellon apprised of sales and Mellon would pay regular visits to London to visit dealers, who would fill their windows with English paintings when they heard the voracious American collector was in town. By 1963, Mellon had enough for an exhibition at the Virginia Museum and brought it to the Royal Academy a year later. It was a rousing wake-up call to the British art establishment, heralded in The Daily Telegraph with the headline, "Mellon show arouses delight and dismay" – delight at the hitherto unnoticed treasures of British art; dismay that they were neglected for so long and allowed to leave Britain. London art dealer Geoffrey Agnew once said of Mellon's acquisitions: "It took an American collector to make the English look again at their own paintings."