A Highgate businesswoman has started an international baking revolution to raise awareness of mental illness – selling grey cakes in pop-up shops.

Emma Thomas, of Tile Kiln Lane, decided to set up a pop-up Depressed Cake Shop in London after reading that one in four people suffer from mental illness at some point in their lives.

But the idea quickly caught on and now pop-up stores are being set up across the country – and all over the world.

Ms Thomas, 32, said: “It’s a really inspiring project. It’s important to open up a discussion about mental illness as people still see it as a taboo.

“If someone breaks their arm, you can see it but you can’t with depression. Doing something with cakes makes it visible.”

She has been inundated with messages from people wanting to set up their own pop-up shop.

Shops are now planned for 19 towns and cities across the UK, as well as globally, with bakeries lined up for Australia, the US and Malaysia.

She insists all cakes and biscuits must be grey, but has left it up to volunteer bakers to decide what they look like inside.

Many of the tester cakes have colourful fondant icing hidden underneath their grey exterior but there are also some “black dog” biscuits, a term used by Winston Churchill to describe depression, and grey macaroons with rainclouds etched on top.

All profits made will go to mental health charities.

Ms Thomas created the project through her own PR company, Cakehead Loves, based at her Highgate home, which promotes brands and charities creatively – often through food and drink.

Eager amateur and professional bakers, many of whom have experiences of mental illness, have signed up to produce homemade goods for the stores as well as offering to run them.

The London shop will be hosted at Suzzle, a coffee shop and art gallery in Brick Lane, over the course of three days on August 2, 3 and 4.

Although the shops are temporary, Ms Thomas wants to keep the project going.

She added: “In the long-term, we plan to carry on and speak to larger charities to create a brand of grey cakes in order to promote an awareness campaign.

“I want to make people see that supporting mental health charities doesn’t have to be serious and that we are allowed to have fun. Everyone has responded really well to the project.”