Gang steals £20m from Milan's 'jeweller to the stars' - but Tilda Swinton saves the best piece

Gem designer Damiani is favoured by a host of stars, including Brad Pitt, Jennifer Aniston and Gwyneth Paltrow.

It also supplied the remarkable diamond-studded bracelet won at Oscars by best supporting actress Tilda Swinton - a stroke of luck for Damiani.

The seven-strong band of criminals – who were unarmed - made off with the haul after tunnelling though a cellar.

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1,865 reasons to be thankful: Tilda Swinton wearing Damiani's Sahara bracelet - 1,865 diamonds hand set in 18-carat white gold. Damiani said: 'Thankfully the most precious pieces were on loan at the Oscars'

They began digging over the weekend after hiding in an empty building next door to the Damiani showroom in what police believe may have been an inside job.

One detective involved in the inquiry said: "This sort of job with this size of haul always has a hand from some mole on the inside."

They emerged through the tunnel dressed as policemen and, once inside, told a handful staff who were preparing for an Oscars party that they were financial fraud officers there for a spot check before tying them up with plastic cable and "emptying dozens upon dozens of boxes" of jewels.

They then locked everyone in the bathroom, except the manager whom they forced to open the safety deposit room where they helped themselves to gems.

The pieces taken were all studded with diamonds and made up of white gold and yellow gold and included earrings, necklaces, bracelets and rings.

However, they missed out on the chance of swiping probably the most valuable piece of jewellery by Damiani as it was being worn by Oscar-winner Tilda Swinton while the raid was taking place.

The bracelet - called the Sahara bracelet - consists of an amazing 1,865 hand-crafted diamonds and set in 18-carat white gold.

Director Silvia Damiani, speaking from Los Angeles after being told of the theft, said: "Thankfully the most precious pieces were on loan at the Oscars.

"I am in complete shock - when I heard the news my legs started to tremble but thankfully at least no staff were hurt.

"Although unlucky we were at the same time lucky as the most important piece was being worn by Tilda Swinton.

"We must still go forward, even if this has left me deeply disturbed."

Later, a Milan police spokesman said: "The gang all wore dark sunglasses and spoke with southern Italian accents.

"They were unmasked and also unarmed - whoever did this job was very professional. The whole thing was over in minutes.

"They had tunnelled through into the shop from a building next door and we think they must have been there the whole weekend - if not longer."