Thursday May 29 - 9:30pm (PG)

Tonight on Trinny and Susannah Undress the Nation, the girls set out to educate women about the shape of their bodies. They firmly believe women need to dress for their shape and not their size.

To illustrate their point, Trinny and Susannah begin their mission in Swindon. They pack the town hall with 50 size 16 women of all ages and put them in identical white shift dresses – size 16 is now the average dress size for women in the UK.

“You might be a size 16 on your tits, you might be a size 16 on your arse,” says Susannah, “so it’s about your shape not about your size. Each dress is exactly the same and we’re going to see how it fits all of you in a different way.”

Out of the 50 women, Trinny and Susannah spot only two ladies who fit properly in to the shift dress. They all wear a size 16 but their bust measurements range from 34 to 48 inches, and their hips from 38 to 52 inches.

Their mission is to educate women that their bodies always fit into one of twelve body shapes and to show women how to dress to flatter those different shapes. But before they do that, they take a 3D look at their own body shape thanks to new imaging technology. They both wear a dress size 10, but have completely different body measurements. Although Trinny is astounded to learn that they have the same length legs – even though she is three inches taller than Susannah!

The 12 body shapes are broken down into 4 main groups – Apple, Hourglass, Triangle and Pear.

100 women are invited to an art gallery with plinths exhibiting the different shapes. Trinny and Susannah find examples of each shape amongst the ladies to help illustrate them and used as a guide before the ladies head off on a mass shopping trip.

After learning the rules, the ladies are challenged to shop for their shape on Guildford high street, and those who get it right will get their money back from Trinny and Susannah.