“I certainly don’t believe in returnism, as it were,” he said. “I don’t think that’s sensible.”

David Cameron's interesting excuse on why he doesn't think the Koh-i-noor diamond shouldn't be returned to India. 
Jewellery and gem stones are often objects of dispute and the ownership decided in court, here is a small selection.

The Koh-i-noor diamond currently on display at the Tower Of London

This ancient diamond, the Koh-i-noor, first recorded in 1306 has a considerable history , known to have come from one of the earliest regions in the world to mine diamonds; the Golconda Kingdom in India.  It was originally 793 carats when uncut. It has never been sold but possession gained in the course of rebellions, wars, invasions and uprisings. You can read more here. In 1849 the British Empire's East India Company confiscated the Koh-i-noor Diamond as compensation for the Sikh wars and presented it to Queen Victoria. Despite repeated requests for its return to India, it remains in the Tower of London as property of the British Crown and is currently set in the Maltese Cross at the front of the crown made for Queen Elizabeth the Queen Mother and can be seen in the Tower of London.

Actress Linda Christian and husband Tyrone Power

Someone who did believe in "returnism" was actress Linda Christian (1923- 2011), albeit with a little financial sweetener. She is credited with being the first ever Bond Girl - “Valerie Mathis” in a TV adaptation of Ian Fleming’s first Bond novel, Casino Royale, in 1954. She was married to the movie star Tyrone Power in 1949, they had two children together before their divorce in 1956. In 1955 she was given a gift of jewellery from an admirer, socialite Robert H Schlesinger, however the cheque for $132,000 that he had given to Van Cleef and Arpels of New York as partial payment bounced. She refused to return them stating they were a christmas gift. However, lawyers managed an amicable agreement where Ms Christian returned the jewellery and was given an undisclosed sum for the "inconvenience".

A pensive Princess Diana wearing a Tiara

What about when a gift only means a loan - a newspaper article from May 6th 1996 reports how Princess Diana being increasingly frustrated by the delay in her divorce from Prince Charles, threatened to sell some of her jewellery. She believed that as they were given to her as gifts at her wedding they belong to her, however the Queen insisted that as they were Royal Heirlooms they must remain with the Royal Family. The items included a tiara estimated at the time to be worth £2 million. She was protected by British Law regarding her famous engagement ring. The UK legislation under Section 3(2) of the Law Reform (Miscellaneous Provisions) Act 1970 (2) states that the gift of an engagement ring shall be presumed to be an absolute gift; this presumption may be rebutted by proving that the ring was given on the condition, express or implied, that it should be returned if the marriage did not take place for any reason. On the 13th of July 1996, almost 15 years after their wedding Diana and Charles announced that they had finally reached an agreement on the terms for their divorce, including Diana being given the right to keep all the jewellery bestowed to her.

Some of Imelda Marcos's baubles

How about you pilfer from your countries treasury and use the funds to purchase high value properties, works of art, jewellery as well as a large shoe collection for yourself, to whom does that jewellery ultimately belong? Imelda Marcos, wife of Ferdinand Marcos (president of the Philippines)  as well as her amazing shoe collection amassed a huge collection of jewellery known as The Roumeliotes, Hawaii and Malacanâng Collections. In February 1986 Ferdinand Marcos was ousted in a "People Power" revolution. Ferdinand and Imelda along with their family and entourage scarpered to the U.S.A. It was reported that U.S. Customs agents discovered 24 suitcases with gold bars and diamond jewellery hidden in them and in addition, certificates for gold bullion valued in the billions of dollars were allegedly among the personal properties.
Philippine investigators estimated their wealth over £6.2 billion.
The next president, Corazon Aquino, set up a special commission to recover these funds for the treasury - but now, more than 25 years later, just over £2.5 billion has been accounted for. Imelda's jewellery had been languishing in a bank vault for decades after being seized. The Sandiganbayan, the Philipine court, in January this year forfeited in favour of the Philippine government the Malacanâng collection of former First Lady Imelda Marcos. In its ruling, the court said this collection is also part of the ill-gotten wealth of the late deposed President Ferdinand Marcos and his family. However, the Marcos's are now disputing the ruling, The heirs asked the court that they be given ample opportunity to prove that the jewellery may have been lawfully acquired through other means or acquired prior to the late dictator’s tenure, so the fight continues...

See some of the collection here

The disputed Bahia Emerald

Heard of the Bahia Emerald? A 3ft tall, 840lb rock embedded with 9 large emerald crystals ranging in size from 220mm, 140mm, 130mm, 110mm down to 37mm -  weighing 180,000 carats in total. It was discovered at the Bahia mine in Brazil back in 2001. Valued at nearly £250 million it has had a remarkable journey, transported to the USA, hidden in an abandoned petrol station, stolen, recovered, submerged in a vault during hurricane Katrina, used as collateral in a diamond deal and at one point even put up on Ebay with a buy now price of £45 million – bargain!.
Legal possession of the Bahia Emerald has changed hands several times, according to some reports, the Bahia Emerald was even involved in a $197 million banking transaction with the notorious Bernard Madoff before he was arrested for committing the largest financial fraud in U.S. history.
At one time eight individuals laid claim to the Bahia Emerald, now just two claimants remain awaiting yet another judgement.The National Geographic Channel have made a documentary about it and there is also a book available. Read more here 

The Aurora Pyramid of Hope - can be seen at the Natural History Museum

Aurora Pyramid of Hope

On permanent loan in “The Vault” at London's Natural History Museum is the Aurora Pyramid of Hope. A display of 295 differently coloured diamonds, 267 carats in total. Only 1 in 10,000 gem-quality diamonds is coloured. The collection was put together over a period of 25 years by two New Yorkers  - Alan Bronstein and Harry Rodman. Named after the Aurora Borealis for the colours and Aurora the Roman goddess of the dawn to symbolise a new beginning and to protect our natural heritage for the future. After the death of Mr Rodman aged 99, it became the subject of court battle between the 2 families. In 2001, at 92, married Mr. Bronstein’s 81-year-old mother, Jeanette, his longtime friend and neighbour, it was she who introduced Harry to her son Alan, and then further complicated by the fact that Mr. Rodman made seven wills in the last decade of his life. In their lawsuit, several of Mr. Rodman’s heirs — a grandniece and four grandnephews — argue that the Bronsteins took advantage of an elderly man and duped him into signing away his interest in Aurora Gems for $10,000. They tried to prove that Jeanette Bronstein had married Harry Rodman for his money. A lawyer who drew up Mr. Rodman’s wills testified on Mr. Bronstein’s behalf stating that “Harry described him as a friend and the son he never had", the judge ruled in favour of Alan Bronstein. The Rodman heirs plan to appeal the decision.