The Tories' new first lady has been loaned designer clothes worth thousands of pounds by the Queen's favourite couturier so that she can accompany her husband to official engagements.
Betsy Duncan Smith, widely admired for her elegant though understated style, has been borrowing suits and cocktail dresses from the Savile Row house of Hardy Amies.
It emerged yesterday that Mrs Duncan Smith, a seventh cousin of Princess Diana and the daughter of a hereditary peer, has had a private consultation with the fashion house's vendeuse.
She borrowed smart designer suits worth between £1,000 and £3,000 and cocktail dresses with a similar value to attend evening functions with the Tory leader.
The high-class clothing deal was declared by Mr Duncan Smith in the latest edition of the House of Commons register of members' interests.
It was arranged by his brother David, 51, who recently took over as chief executive of Luxury Brands Group, which owns Hardy Amies, after moving from Prada. He said yesterday that his sister-in-law borrowed clothes "from time to time".
Friends of the family insisted the arrangement was likely to continue for the foreseeable future. "She looks absolutely fabulous," said one. The Tory party refused to comment.
The Conservative leader has been eager to keep his family out of the limelight since taking over from William Hague and has criticised Tony Blair for "ruthlessly" using his family to win public support. Betsy Duncan Smith – said to be a size eight – has shunned publicity and only attended her first Tory party conference last year after her husband was made party leader.
Mr Duncan Smith refuses to allow his four children – Edward, 14, Alice, 12, Harry, 11, and Rosanna, eight – to be photographed by the press.
Yesterday a spokeswoman for the Luxury Brands Group, which recently took over Hardy Amies and Norman Hartnell, the Queen Mother's favourite designer, confirmed Mrs Duncan Smith had borrowed clothes after discussions with its experts.
"We have lent her a couple of suits and some evening wear. She borrows from time to time," she said. "She's a really perfect size for couture, which tends to be small."
Suits from the Savile Row tailor cost between £1,000 and £3,000, with evening wear, depending on its intricacy and the amount of detail such as beading, costing upwards of £1,000.
Hardy Amies, founded in 1945, has dressed the Queen, the Queen Mother and Princess Margaret. The couturier has displayed the Royal Warrant since 1955, two years after designing the Queen's Coronation gown.
Since the 93-year-old Mr Amies retired, his company has remained the Queen's favourite dressmaker. Its collection for the Queen's recent Golden Jubilee tour of Jamaica was hailed as a "sartorial coup". But Jon Moore, who designed the nine outfits for the Queen's Caribbean visit, as well as the suits and dresses worn by Mrs Duncan Smith, has recently been replaced by Jacques Azagury, a favourite designer of Princess Diana.
Moroccan-born Mr Azagury has also dressed TV presenter Ulrika Jonsson and the singer Sophie Ellis Bextor, and will be in charge of modernising the brand and seeing through its new ready-to-wear collection launch this year.
In the register of members' interests, the Tory leader reveals that "my wife has been lent clothing to wear at official functions which she has attended in her capacity as wife of the Leader of the Opposition. This benefit has been provided by Luxury Brands Group".
Hardy Amies is not the first fashion icon to have been linked to Iain Duncan Smith. He also took a donation of £20,000 to help his campaign to become Tory leader from John Frieda, the celebrity hairdresser.Reuse content