If you’ve been enjoying Hampstead Heath this summer, you may have come across an unusual slab of concrete amongst the greenery.

This is because a Belsize Park man has been leaving concrete doorstops for members of the public to take home as part of a free, Instagram-aided treasure hunt.

The concrete comes from furniture makers Jonny Concrete, who thought it would be a fun way of using up the excess that is a fact of live in when you make concrete furniture.

Jonny from Jonny Concrete - who lives in Belsize Park but works out of a workshop in Acton - told the Ham&High: “I couldn’t really say how or when we came up with the idea - it just happened and seemed like a great way of using the left-over concrete.”

“For various reasons you can never pour exactly the right amount of concrete, and you never like to see it thrown away so this was how we decided to use it.”

Jonny added that the initiative has gone down really well, particularly on the Heath.

He said: “It’s a bit of fun, we’ve seen people really enjoy finding one after a hot and boozy day on the Heath. We’ve found the reaction varies over London, they get far more engagement there than, for example, in the City on a weekday.”

The concrete doorstops are the by-product of Jonny Concrete’s main business, creating concrete tables, but the company sells them individually too.

Since July, Jonny has been using Instagram to make the doorstop giveaway into a treasure hunt. He posts a picture of a doorstop and leaves it up to his followers to hunt for where exactly it is.

He said: “The Instagram @JCdoorstop has gone down pretty well, it’s a way of engaging with customers and we’ve found each weekend we get ten or twenty new followers - usually because one person in a group has found one and mentioned it to their friends.”

“The Heath is the main place we leave them because it’s so convenient and in the weather we’ve had, so many people have been enjoying the space.”

The doorstops come with a label which congratulates those who find them and encouraging hunters to share photographs of their bounty on social media.