An amethyst ring Margaret Thatcher wore the day she entered 10 Downing Street as the UK's first female Prime Minister has sold at auction for £27,500.

The ring was one 170 of the Iron Lady's personal possessions to go under the hammer earlier this month at Christie's in the Mrs Thatcher, Part III, online sale.

The auction coincided with the 40th anniversary of Margaret Thatcher's election as the UK's first female Prime Minister (1979-1990), and was the third and final of a trilogy of auctions held as part of the arrangements following her death in 2013.

The Part III lots sold for a total of £1,087,750.

Evocative items of note included her 'uniform' jewellery given to her by her husband Denis, comprising not only the 18-carat gold amethyst ring but also a hardstone 'pebble' bracelet with six cabochon stones set between gold links.

The bracelet had an estimate of £1,500 to £2,500, but was sold for £40,000 - 26 times its lowest estimate.

"The success of this lot illustrates the overwhelming appeal of strong provenance," says specialist Adrian Hume-Sayer, referencing the many photographs in which Mrs. Thatcher can be seen wearing the bracelet.

"It's unquestionably that tangible link with so many important moments in 20th century British politics that led to this fantastic result."

The ring or bracelet were worn for almost all occasions, from the day Mrs Thatcher entered Number 10 Downing Street on 4 May 1979, to her historic meetings with global figures including Mikhail Gorbachev, Ronald Reagan and Nelson Mandela.

The numerous other treasures included a typed list of Prime Minister's Engagements from her final day in office which sold for £10,625.

The Margaret Thatcher sales began in 2015 when Part I and Part II attracted a global audience, with all lots sold for a total of £4,516,038.

Born on October 13, 1925 in Grantham, Mrs Thatcher was the daughter of local grocer Alfred Roberts who was also a local politician and twice became the Mayor of Grantham. She went first to Huntingtower Primary School and then Kesteven & Grantham Girls' School.

Photos: Christie's