In January 1779, the Westmorland, an armed merchant ship sailing from Livorno to London laden with the mementoes of wealthy young men on the Grand Tour, was captured by two French frigates and declared a ‘prize of war’. Towed into Malaga, its cargo — 90 crates of antiquities and works of art, souvenirs ranging from Piranesi engravings and Cozens watercolours to books, maps, and fans, as well as anchovies and 32 wheels of Parmesan cheese — was seized and sold on in Spain. Most were bought for King Carlos III of Spain, and over time the contents dispersed across Spanish museums. Nothing reached these shores.

Until now: 233 years later, as the result of painstaking detective work from a team of Spanish scholars, beginning late 1990s, to trace the original owners’ identities and the fascinating stories behind the objects. The Ashmolean Museum’s major exhibition this summer has 140 objects from that fateful voyage on view to tell the story of The English Prize.

Each crate was meticulously listed, each item marked with ‘P.Y.’ What that meant became forgotten, but the research revealed that it stood for ‘Presa Ynglesa’ (‘The English Prize’).

The English Prize: The Capture of the Westmorland, An Episode of the Grand Tour is a multi-layered show. The triple-barrelled title hints at that, as does the giant tome of a catalogue the scale of the research.

Taken at one level, it’s a tale of piracy (albeit to take an enemy vessel as a prize of war was lawful at the time). At another, it offers a unique snapshot of the Grand Tour: what these British tourists aspired to, shopped for, in order to show off their good taste and erudition once home; what sights affected them (in his guidebook, John Henderson noted the date he first arrived in Rome at the Porta del Popolo, clearly an important moment for this future Scottish baronet).

For many, a marker of this elite trip was to have a likeness made in Rome, by the best portrait painter affordable. Francis Bassett, heir to a Cornish tin-mining fortune, a big spender with many art possessions on board, had a full-length portrait by Pompeo Batoni.

It is a typical Grand Tour portrait (see right): he stands elegantly, surrounded by antique fragments with St Peter’s Basilica as a landmark in the background. Another portrait, of a beautiful young man, offers a touching note. It is small and not at all typical of a portrait brought back from the Grand Tour; it’s also framed (unusual in transport).

It was in Henderson’s crates, though is not of him, and it seems he was particularly keen to recover it, “a portrait he joys, which he wishes much to have”. The sitter remains a mystery.

n Until August 27. A Grand Tour Trail around the rest of the museum neatly links exhibition and objects in the permanent collection. For exhibition tickets, events, and catalogue details, see: www.ashmolean.org/exhibitions/