The size 6 singer-turned-fashion designer says she uses her own body to see how her designs will look on anyone who isn't a model.
She said: ''We always joke that we have this fabulously gorgeous 17-year-old model who is six-foot-whatever and then I say 'Okay, I'm going to put it on. I stand for the general public here'.
''It's how I work. I found it really difficult when I was pregnant and I couldn't do that. It's part of the process - I'll stand here in my knickers and start draping fabric over myself. It was very hard when I didn't have my body.''
The working mother-of-four broke down in tears when she won Designer Brand of the Year at the British Fashion Awards last November - but insists it gave people a chance to see the ''real'' her.
She told Harper's Bazaar: ''When they read my name, I was genuinely not expecting it. It was like my heart was going to jump out of my body.
''I came offstage and said, 'I cried three times, I didn't thank the people I wanted to thank, I was really rubbish'.
''But I think people saw the real me ... and the truth is, I would have felt much more comfortable in my pyjamas with the kids and [husband] David in a hotel watching it on TV.''