Revd Joanna Jepson, an Anglican priest and Chaplain of London College of Fashion, told Premier's News Hour: "I think the evidence would show that people are affected by what they see."
"It's a very dangerous thing for them to be doing and very irresponsible."
Topshop has promised to stop using unrealistic mannequins after a customer posted a complaint online about the skinny models, which went viral.
Laura Berry posted an image on the internet and called the mannequin 'ridiculous'.
Topshop has admitted the mannequin is very tall for 'more impact', and says it will not order any more.
Revd Joanna Jepson told Premier fashion is meant to be inclusive: "I think it's incredibly dangerous as Topshop is a leading brand and it's incredibly influential in the world of fashion, in high street retailing and young girls and grown women look at Topshop's clothes and advertisements and will really pay attention to what they're putting out there.
"And if they're distorting images and suggesting that an average shape is something that it shouldn't be, and isn't average, then I think that's going to have a knock on effect, distorting young women's perceptions of what is normal and what is acceptable, and what you have to be in order to enjoy fashionable clothes."
Topshop said in a statement that it had long "made it a priority to showcase a healthy size image."
"The mannequin in question has been used in stores the past four years and is based on a standard UK size 10.
"The overall height, at 187cm, is taller than the average girl and the form is a stylised one to have more impact in store and create a visual focus.
"Mannequins are made from solid fibreglass, so in order for clothing to fit, the form of the mannequins needs to be of certain dimensions to allow clothing to be put on and removed; this is therefore not meant to be a representation of the average female body."
Listen to Premier's Hannah Tooley speak to Revd Joanna Jepson here:
