How Maggie learned to power dress until she was even considered sexy

As Prime Minister she was a born leader but Margaret Thatcher's fashion sense did not come quite so naturally, the woman who recreated her wardrobe for the big screen said today.

Jane Law, costume maker for biopic The Iron Lady, starring Meryl Streep, said that although she got the hang of it later on, Baroness Thatcher looked as if she were "going to a wedding" when she first entered Parliament.

Ms Law said she was forced to change her image dramatically because people were paying too much attention to her hats - which she used to pair with suits and matching gloves and shoes - instead of what she was saying.

The film, which premieres tonight, tells the story of the former leader's journey from grammar school girl to prime minister through a series of flashbacks.

Ms Law, from Worthing, worked with Oscar-nominated costume designer Consolata Boyle to recreate Baroness Thatcher's outfits to make Streep look as convincing as possible.

They looked at photos and newsreels from the Seventies and Eighties, using a magnifying glass to study the clothes right down to the stitching.

"She definitely changed her image over the years," said Ms Law. She obviously felt in the beginning that going to Parliament was an event so she did look like she was going to a wedding.

"But it was necessary to change her image because people were paying too much attention to her hats."

With the help of an adviser from Aquascutum, Baroness Thatcher's favourite fashion label, her style evolved during her tenure and she went on to develop her own power-dressing style. She sometimes commissioned Aquascutum to make several of a particular garment if she found something that she liked.

But she also had her girly side: she especially liked to wear bows, and two of her favourite items were a bangle with multi-coloured gem stones, which she always wore, and a pearl necklace. Both items of jewellery were gifts from her husband, Denis.

Ms Law, whose previous credits include Pirates of the Caribbean and Shakespeare in Love, claimed highly intelligent women like Baroness Thatcher often weren't as interested in fashion as others: "She had other priorities. She was very cerebral and although she knew image mattered, it wasn't all about the outfit.

"Like Hillary Clinton and Cherie Blair, she is a woman who lives very much inside her head," she said. "They feel they can take or leave shopping. They didn't enjoy clothes to the same extent as Samantha Cameron."

Nevertheless, said Ms Law, Britain's first female PM did develop her own power-dressing style, adopted by other women. "The Seventies was an awful, ugly period for fashion. Her power-dressing period that followed was quite a good one. Once she got the hang of it, there was no stopping her. Then people decided she was sexy, and she became rather attractive."

Ms Law said a highlight had been recreating the outfit Baroness Thatcher wore the day she was elected in 1979: a radial pleated skirt and a blouse with a Peter Pan collar that was "slightly too big": "I couldn't take my eyes off that outfit, and I took great pleasure in repeating the collar."