Elle Macpherson has toughened up for the new series of Britain and Ireland's Next Top Model, according to co-host Julien Macdonald.

The designer said the Australian model had to change to cope with the arrival of Whitney Port and Tyson Beckford from the United States, who are joining the judging panel.

Julien said: "She's a bit tougher this season. She had two new judges to compete with and the thing with these Americans is they're loud and they shouted, there was lots of times when we said, 'You Americans, shut up'."

The series, which launches on July 9, will also feature appearances by models Andrej Pejic, Erin O'Connor and Tali Lennox, Britain's Got Talent judge Alesha Dixon and former Spice Girl Mel B.

Other celebrities who will be guest judges during the 12-week competition include Pussycat Doll turned Got To Dance judge Kimberly Wyatt and style icon Poppy Delevigne.

The contestants will compete to win a contract with international agency Models 1, a cover and feature in Company magazine and a contract with Revlon cosmetics.

Elle said the panel's role was to "mentor these girls".

She said: "It's not about criticising or putting them down, it's to encourage them and the fact they've got to the stage which they are in the competition means they are beautiful and they have charm and presence so we focus on 'what are their strengths?' and we can give them tips on how to work in a way that brings out the best in themselves, that's what we do.

"It's not really about telling somebody, 'Your legs are short', it's about saying, 'actually if you sit in a certain way your legs look longer' because that's important in this business."