ON A summer’s day in 1912 demolition workers broke through the wooden floor of a building in Cheapside, the main thoroughfare in the City of London, and struck gold. In the stone- and brick-lined cellar lay sparkling treasure. Caked in earth were 500 gold bracelets, rings and necklaces set with precious stones; ancient cameos and intaglios; earrings dangling with bunches of amethyst grapes; long, dainty chains with links of enamelled daisies or roses; and fashionable brooches including an engaging enamelled lizard set with Colombian emeralds (pictured).

The workmen had stumbled on the stock of a 17th-century goldsmith. Undeterred by who owned it, they scooped up as much as they could carry and went across the river to the bric-a-brac shop of George Fabian Lawrence. Stony Jack, as he was called, was known for his willingness to pay cash for whatever builders found. But this haul was more than he could handle. He contacted the aristocratic trustees of the embryonic London Museum, who agreed to buy the lot.

The workmen, Stony Jack and the trustees were all aware that they were dealing in goods to which they had no legal right. Yet their shady actions ensured that the world’s largest collection of Elizabethan and Jacobean jewels survives intact. Known as the Cheapside Hoard, these rare treasures are being exhibited together for the first time at the Museum of London.

The stretch of Cheapside where this cache was buried was known in the 17th century as Goldsmith’s Row. The exhibition recreates the kind of prosperous workshop where jewels would have been made and sold. (The museum also holds the biggest collection of goldsmiths’ tools in England.) Against this backdrop is a lavish parade of rings, brooches, earrings and other ornaments. Unlike the royal jewels of this era, these pieces are subtle rather than flashy. The craftsmanship is remarkable and well worth closer study through the magnifying glasses provided.

The show includes oil portraits from this period featuring elegant women wearing gold enamelled chains, singly or in tiers looped across their bodices. Only 30 examples of these delicate necklaces survive, and they are all on display here.

Hazel Forsyth, the curator, spent years studying letters, stock lists and rent books as well as the objects themselves. Her patient scholarship has unearthed plenty of dubious behaviour, much of it chronicled in her excellent book, “London’s Lost Jewels”. Apparently the original London Museum cunningly wooed royals to help hold on to its hoard, and much of the gold itself is 19.2 carats, at a time when 22 carats was the legal standard. This feast for the eyes has quite a story to tell, as well.