Bob Hall is the man in charge of one of the country's best-loved open spaces: the swathe of rolling hills, forest glades and secluded ponds that make up Hampstead Heath.
But Mr Hall does not like what he sees. The heath - dubbed the "green lungs of London"- is also the gay cruising capital of the world. According to Mr Hall, the men who go in search of casual sex among the trees are turning parts of the heath into "no-go areas" for other visitors.
Traditionally, cruising has been concentrated in an area called the West Heath, but wardens are now forced to clean up used condoms, packets of lubricant and other "sexual detritus" throughout the heath, said Mr Hall, chairman of the heath's management committee.
Last year, the City of London spent £40,000 removing condoms and other sex-related waste from the area. Meanwhile, bathers at the Hampstead swimming ponds complain that sexual activity in the area is driving away other swimmers and families.
"We accept that cruising takes place on the West Heath, but it is completely unacceptable beyond there. We will certainly not tolerate the kind of behaviour that goes on in the men's bathing area," Mr Hall said.
Bordered by some of the capital's most exclusive neighbourhoods, the heath has long been a favourite spot for gay assignations. For the most part, police and local authorities have turned a blind eye, but that uneasy truce is now under threat, Mr Hall said.
Peter Tatchell, of the gay rights group Outrage, accused wardens of hypocrisy for ignoring straight couples who also indulge in outdoor sex. "The management of the heath is obsessed with gay cruising and totally ignores heterosexual sex," he said.
Neil McGuinness from the Terrence Higgins Trust, said: "I wouldn't say that [gay] sexual activity has spread. If there is sexual detritus then possibly there are some people having sex - but is it gay sex?"
In the new British film Scenes of a Sexual Nature, Ewan McGregor plays a gay man who picks up potential lovers at the heath's bathing ponds - a scene which bathers say is re-enacted almost every day in real life. Jeremy Wright, who lives near the heath, said: "We're not trying to drive the gays out, we just want them to temper their behaviour."
After he was photographed allegedly cruising on the heath, George Michael defended the practice as part of gay culture.