The steady stare with which Andy Warhol surveyed the world was commented on by all who met him. His was the all-appraising eye of the artist as observer.

The result of his observations came in remarkable paintings and other works that chronicle, among much else, the gilded age of late-20th-century celebrity culture in which he played a prominent part.

More than 100 of these – all, astonishingly, in the same ownership – are arranged to compelling effect in the Andy Warhol exhibition that has just opened at the Ashmolean Museum.

They belong to American-based hedge fund manager Andrew Hall, who studied chemistry at Keble College, Oxford, between 1969 and 1973, and rowed four times in the Varsity crew.

At the private view last week, Sir Norman Rosenthal, the show’s curator, rightly praised him and wife Christine for their generosity in allowing the removal of so much from the walls of their home.

The rooms are hardly going to be bare, however, since the Halls’ collection – made available to many public institutions in the past, including the Ashmolean – includes work by lots of other artists.

Among them are Joseph Beuys (who appears in the new show in a series of screen prints), Georg Baselitz, Anselm Kiefer, Franz West, Malcolm Morley, Arnulf Rainer, A.R. Penck, Eric Fischl and Peter Saul.

Andy Hall, an affable figure moving among guests at the opening, was en route to Germany and the castle he owns at Derneburg, formerly the property of Georg Baselitz, which is shortly to become a public museum.

I asked which Warhol was his favourite, on which he declined to be drawn. “I like them all,” he said, which, if you think about it, is presumably why he bought them

In an interview with gallery director Xa Sturgis that appears in the catalogue, Andy said: “I think he is one of the most important and influential artists of our era. He influenced pretty much everybody who came after him.”

Norman Rosenthal holds a similarly high opinion. “Evermore, Warhol feels like the decisive artist of his generation who peered into the future and saw his world with all its glamour and its horror.

“The Halls’ collection of Warhols demonstrates the artist’s extraordinarily diverse output, as he reacts to his world with penetrating truthfulness and wit.”

On the press tour of the show, Norman told us: “Andy was right. Every picture has its rightness, and sense of time. He wanted to be a prophet.”

Though Norman’s catalogue essay is entitled “Meeting Andy Warhol”, his own occasional encounters with the artist are not chronicled.

I had to wait for Saturday evening’s Loose Ends on Radio 4, when Norman was a guest, to learn that Warhol wanted to paint him – an invitation he declined.

“He wanted to take all my clothes off, to see me naked,” Norman told presenter Clive Anderson. “I was a pretty boy in those days.”

Andy’s admiration for the male physique is evident in one daring full-frontal image in the show, Nude model (male), from the Torsos/Sex-Parts series that Warhol began in 1977, deriving great voyeuristic pleasure from their creation. These were not shown during his lifetime.

Master printer Rupert Smith, who worked on these silk screen works, said Warhol avoided touching his subjects.

He told Andy’s biographer Victor Bockris: “He was just so scared of physical contact. There were nights in Studio 54 [the hot disco of the day] when these humpy well-built numbers jumped all over Andy, like ‘I’ll do anything for you . . . possibly’ and he just wouldn’t know what to do; he’d just get freaked out.

“So this was his way. Victor Hugo [a pal of Andy’s] would pick up some hot number on a bar or in the street and Andy, the voyeur, would click click click away.”

From the same period, with no less determination to shock, come seven of Warhol’s ‘Oxidation’ paintings, in the creation of which the artist and his associates took turns urinating on to canvases coated with wet copper paint.

“Unfortunately,” wrote Bockris, “the ‘Oxidation’ paintings retained the lingering odour of their main ingredient.”

Prospective visitors to the Ashmolean show, which continues until May 15, might welcome my assurance that this appears no longer to be the case.