Sarah Brown, the Prime Minister's wife, has resorted to renting expensive designer clothes for official functions, it has been disclosed.

Mrs Brown pays hundreds of pounds of her own money to rent the items - including a £9,000 top worn at last week's G20 summit events with other leaders' spouses.

Mrs Brown's approach is in stark contrast to that adopted by her predecessor, Cherie Blair, who was criticised for receiving free clothes or discounts worth thousands of pounds from top designers. Carole Caplin, Mrs Blair's lifestyle guru, is said to have negotiated many of the discounts amid concern from senior civil servants at the time.

For recent banquets with foreign leaders and the Lord Mayor, Mrs Brown has rented dresses from Amanda Wakeley, the British designer. She wore one of Amanda Wakeley's dresses for the state banquet with the President of Mexico last week.

She is also understood to have rented dresses and jackets from Brett Lintner and Graeme Black - including a jacket she wore to the official G20 summit dinner.

The rentals typically cost about 10 percent of the retail price which means that Mrs Brown regularly incurs bills running into hundreds of pounds for her outfits. The money cannot be recouped.

Mrs Brown is said to usually wear clothes from high-street retailers such as Marks & Spencer and New Look. However, a friend of the Prime Minister's wife, said: "Sarah thinks it's important to dress well for big State occasions, and renting her dresses makes that a bit more affordable."

Mrs Brown was a successful public-relations executive who owned her own company. However, she gave up paid work when her husband was Chancellor to avoid any conflict of interest. She is thought to have taken out a mortgage on a flat owned by the couple which helps fund her spending while her husband remains Prime Minister.