Thieves climbed a two-metre high wall to steal antiques from the country home of a multi-millionaire entrepreneur.
The four suspects, who were captured on CCTV, raided the home of Prof Sir Christopher Evans in Bibury, Gloucestershire, on 9 July and took diamond rings, tiaras and bracelets.
The theft had a “devastating” effect on Sir Christopher’s wife, Lady Anne, due to the sentimental nature of the items.
A “substantial cash reward” has been offered for information.
The CCTV footage captured the gang carrying items in a log basket across the grounds before putting them in a silver or grey Audi S5 and heading towards Cirencester.
Antique items taken include diamond rings, gold brooches, a tiara, a Cartier bracelet, a choker, silver candlesticks and three Art Nouveau silver rose bowls.
It is estimated the items stolen in the burglary – which happened between 17:00 and 20:00 on Monday 9 July – have a value of at least £1m.
In a statement, Sir Christopher, an internationally renowned life sciences entrepreneur, said: “The real pain comes from what these stolen items mean and symbolise in our lives.
“Anne’s engagement ring was her late father’s signet ring – the only thing she has left of him. The diamond ring I bought my wife when our first child was born cost almost our entire savings at that point.”
He added the couple had “always taken security around the property very seriously and we have obviously stepped up security with 24-hour dog patrols around the property”.
Det Con Faye Satchwell-Bennett, from Gloucestershire Constabulary, said the burglary has had a “marked impact” on the victims, and asked that antiques dealers to be on the lookout for any of the items.