An elderly woman was left shocked by a teenage couple engaging in a lewd act in the middle of a park often used by toddlers and their parents.

Bridie Redmond, 67, of West Hampstead, said her sunny afternoon walk around Golders Hill Park on Hampstead Heath was ruined when she came across the couple engaging in oral sex on a bench in the middle of the day on April 27.

Ms Redmond said: “I was watching the ducks in the park and I noticed a couple sitting on a bench nearby. What happened next was totally shocking. It happened before my eyes in broad daylight.

“The ducks dived for cover, but where were the park wardens?”

She added: “It made me really angry because it’s the most amazing space. I’m not a prude, I’ve raised three children.

“I have used the park for the better part of 40 years – I walked my children there, I have walked my dogs there and my children have walked their children there.

“I have never seen anything like this in all that time.”

Unable to find any Heath constables to report the incident, she returned the next week and spoke with a gardener about it.

Hampstead Heath has its own constabulary and the open space, including Golders Hill Park, is governed by a unique set of bylaws that cover indecent exposure, public propriety and sexual offences, among other things.

Last year, across the whole of the Heath, there were 18 reports of indecent exposure, five reports of exposure with intent to insult a female, and 13 reports of people exposing themselves.

Since January this year there has been one report of intent to insult a female and one report of a person exposing themselves.

Richard Gentry, who manages the Hampstead Heath constabulary, said: “Behaviour which may outrage public decency will not be tolerated.”

He encouraged people to report crimes to the Heath Constabulary on 020 8340 5260 or to call police. The constabulary’s telephone number is displayed on notice boards at the main entrances to Hampstead Heath and Golders Hill Park.