“At the moment, there are far too many loan exhibitions in the world,” he says. “I would like there to be fewer for sure.” Why? “Because I think they have disrupted the balance between enjoying works of art on a repeated basis, [i.e.] enjoying the sense of a permanent collection, and the special exhibition where you understand a particular artist in depth. It’s a very difficult balance to keep. There’s always an excitement about a loan exhibition, but the exhibition mentality pushes art towards theatre.”

Today we take so-called “blockbuster” exhibitions for granted – yet, as Penny is keen to point out, it is only relatively recently that the National Gallery began to stage them with regularity, following the construction of the Sainsbury Wing, which opened in 1991. Moreover, he says, “the majority of our visitors actually come to see the permanent collection – so it would be crazy of us to compromise its character by turning it into a kind of loan bank whereby we could just get more and more great pictures [for temporary exhibitions] from other institutions by lending our own. But if you don’t lend, you don’t borrow – that’s now quite clear.”

Has he taken any steps to remedy the situation? “Yes,” Penny replies, his eyes shining. “When I became Director in 2008, we stopped having three big loan exhibitions per annum and went down to two. They were putting a tremendous strain on the institution.”

“There is an argument that big exhibitions consume a great deal of time, energy and resource, and that they take away from the presentation of a permanent collection,” he tells me. “But I like exhibitions. I’ve always been a bit sceptical of the argument that curators would be producing big catalogue raisonnés if only they weren’t concentrating on ephemeral exhibitions, because I think a great deal of scholarship and research goes into exhibitions.”

Of course, you could say that the man running the Royal Academy would argue this, since the institution has a much smaller permanent collection than the National Gallery, as well as an abundance of exhibition space, which it needs to fill. “In some ways,” Saumarez Smith says, “the Royal Academy is the home of the blockbuster exhibition. When we did The Real Van Gogh: The Artist and His Letters [in 2010], it got more than 410,000 visitors. It was a blockbuster. But it also had a deeply serious purpose. I believe you get a different order of understanding of an artist by seeing their works together. I’m sure there are people who can go from place to place making comparisons by virtue of training and visual memory – but I prefer to see two works next door to one another.”

 “We do send works of art by air freight,” says Penny, “but apart from the risks of aeroplanes crashing, which we all know about, with air travel, because of the security arrangements at airports, it is becoming more and more difficult to have exact control over what happens within cargo sheds and when works of art are put on the plane.”

Saumarez Smith disagrees. “Works of art can be travelled extremely safely,” he says. “There are people who are anxious about the risk, and it is always said that it only requires one aeroplane to go down with a large number of Poussins and the whole ecology of the blockbuster exhibition will change – but so far that hasn’t happened.”