Gardeners' World host Adam Frost says he did not realise his parents were swingers – because they did not grow pampas grass outside their house. The popular TV horticulturist stunned fans when he revealed in a recent podcast that he moved out of the family home in Devon aged 16 after discovering his mum and dad were into couple swapping.

While finding this traumatic at the time, he can now joke about it and during a live theatre event last week quipped: “It was a bit of a shock, I’ll be honest, but part of the reason is there was never any pampas grass in our front garden!” There has been an urban myth since the 1970s about anyone who plants the feathery cortaderia selloana. It was meant to be a secret sign the residents were into “swinging” – swapping sexual partners.

Adam, 55, told the audience: “My mum and dad had got really into village life and they had decided they were going to do a swap with another couple. So what happened was my dad was moving in with this lady. And the fella that the lady was married to was moving in with my mother. I was 16 years old at the time and it blows your world apart."

He added: “In the end it all worked out for them and they stayed married for many years and they were all fine but at the time I was like ‘No. No. No. No. I’m off’. So I moved out and got a little bedsit.”

Adam went on to become a garden designer and after stints on The One Show and The Chelsea Flower Show he landed a post on BBC Two’s Gardeners’ World in 2016.