The Royal Collection has remarkable holdings of Italian Renaissance and Baroque paintings and drawings and, on one level, this exhibition is a spectacular display of many of the established highlights. The great strengths are in the 16th and 17th centuries in fact, there are no works from earlier centuries here. When it comes to paintings, such masterpieces as Lorenzo Lotto’s brooding Portrait of Andrea Odoni and Artemisia Gentileschi’s powerful Self-portrait as the Allegory of Painting are representative examples of the peaks, and the same goes for works on paper such as Michelangelo’s impeccable Fall of Phaeton in black chalk or Raphael’s luscious The Three Graces in red. What makes this show exceptionally memorable, however, is how it combines old favourites with new discoveries.

The most dramatic claims are for two paintings, A Boy Peeling Fruit and The Calling of Saints Peter and Andrew, here attributed to Caravaggio. To have undervalued both in the past may look as Lady Bracknell might have remarked like carelessness, but the truth is that, in both instances, recent conservation work has made them much more legible. As art historians are notorious for shunning easy agreement with the same determination as vampires recoil from garlic, it seems unlikely that both canvases will be universally accepted as autograph originals by the master, but only time will tell.

Other cleanings have not resulted in fresh attributions, but have changed the appearance of major works for the better. The Parmigianino Portrait of a Young Man, which was half doubted in one of the Royal Collection’s own catalogues in the recent past, now emerges as emphatically by the artist.

This is perhaps the place to observe that, throughout the exhibition’s admirable and informative catalogue (by Lucy Whitaker and Martin Clayton, with contributions by Aislinn Loconte), there is evidence of an almost self-flagellating determination not to give works the benefit of the attributional doubt.

In the sections devoted to drawings, the discoveries, on occasion, involve even more dramatic changes of mind. The reasons are straightforward enough, and have to do both with the sheer volume of sheets in the Royal Collection and with the way drawings are stored. They live in boxes, above all to protect them from light. The many thousands of Italian drawings at Windsor have all been catalogued, but only a selection of them is illustrated in the volumes of the catalogue.

It is, therefore, all too easy for them to become, in effect, ‘lost’ under the wrong name. The most telling instance of this process is a black-chalk head study in the present show, entirely convincingly given to the 16th-century Florentine painter Andrea del Sarto, but previously associated with the 17th-century Bolognese painter Guido Reni. In view of the fact that it was mounted for George III among material by followers of Guido Reni, it has taken literally centuries to regain its identity. The same is true of a second sheet here, an arguably even more striking red chalk head by Polidoro da Caravaggio, which languished under the flattering but misleading umbrella of Carracci until it was rescued a few years ago.

It would be wrong to imply that this show is a parade of finds, but the aura of scholarly energy does add to the sense of excitement, and the sheer level of quality whether from household names or artists only their friends and families have ever heard of is dazzling. I have always had a sense that the Queen’s Gallery gets fewer visitors than it deserves, but this exhibition is definitely not to be missed.

‘The Art of Italy in the Royal Collection: Renaissance & Baroque’ is at the Queen’s Gallery, Buckingham Palace, London SW1 from March 30 to January 20, 2008 (www.royalcollection.org.uk; 020?7766 7300)