With its avenue of rustling cedar trees, billowing cow parsley and lush carpets of bluebells and cowslips, Brompton Cemetery in the Royal Borough of Kensington and Chelsea is an extraordinary pocket of peace and tranquillity which balances the roar and rage of west London.

The air smells different. The sound of traffic is distant. Walkers chat. Bumblebees buzz. A young man lies in the sun among the bluebells reading Proust and a fat pigeon pecks at the fresh flowers on Emmeline Pankhurst’s grave.

Idyllic, some might say.

But not in the eyes of the park’s many dog walkers. Not today, anyway. Because most of them are in despair at the news that a dog poisoner is at large, both here in Brompton Cemetery and just over a mile up the road in Holland Park, laying down toxic chicken and waiting for a poor animal to gobble it up.

‘Someone’s poisoning our pets!’ says Becki, who walks Tita, an impossibly tiny chihuahua through the park’s dog-friendly loop at least once a day.

‘I caught her the other day nibbling a chicken bone and I became totally hysterical, though luckily she was fine afterwards.’

Today, thankfully, Tita looks great, trotting about busily with her little pink tongue sticking out, but Becki is still anxious.

‘We’re all frantic with worry, of course we are. Our dogs are everything,’ she says.

Rupina, with Harley Davidson, a black and white shih tzu cross, joins us.

‘A friend sent me a message earlier saying, “Keep an eye on Harley. There have been dead foxes and poisoned dogs”. And our doggy WhatsApp groups have been going crazy,’ she explained.

They’re all sharing the alarming community engagement warning posted by the Metropolitan Police last week.

It urged dog walkers to be vigilant, confirming that chicken thought to have been spiked with toxins had been found in both parks over several days. One dog was reported to have eaten some of the meat in Holland Park and subsequently became ‘very unwell’ and was treated by a vet.

And two seemingly healthy foxes were found dead in Brompton Cemetery with no obvious signs of injury – no cuts, bashes or signs of physical foul play.

So today, instead of any of the usual dog walk chat – about the weather, politics or the price of Lily’s Kitchen designer dog food – all anyone here can think about is the dog poisoner.

‘Whoever it is must be properly evil,’ says Carole, beautifully presented in pearls with a glossy black labrador called Gully. ‘Sick in the head.’

‘What sort of monster would do that?’ says Julia, a former art director for TV and commercials, who is pushing her furry prince, a 16-year-old Tibetan terrier called Zeus, around the park in a smart dog pram while his friend Ralph, a Border terrier, trots alongside with his owner, Alexandra, a beautiful blonde expecting twins in August. ‘But why? Why would someone ever think to do something so awful?’ asks Alexandra. It turns out there are a surprising number of theories.

One recurring theme is the ongoing tension between dog walkers and other cemetery regulars. Because while the cafe sells 65 pence-a-pop gluten and egg-free bone-shaped dog biscuits and there is a dedicated dog walking loop, this is a working cemetery, with freshly grieving relatives.

So it doesn’t help that, despite endless warning notices, not everyone is good at sticking to the ‘dogs only’ areas and keeping their pets on short leads.

‘A friend of mine had a curse put on her dog by an Egyptian family who have a grave on the far side,’ says Becki. ‘There are a lot of very strange people out there and a lot of people who really don’t like dogs.’

Camilla, 67, here with Harry the Bedlington terrier, thinks it’s all par for the course for Brompton Cemetery.

‘Years ago this was a hotbed for alfresco gay sex. You’d see them at it in the cow parsley behind some of the bigger gravestones. Now there are drug dealers in the far corner and the police do nothing,’ she says. ‘Last month, the park was closed because a body was found – a man in his 50s, apparently, but they still haven’t identified him...’

Becki suspects the poison could have been aimed at urban foxes – the scourge of lots of city dwellers.

Others think it can only be the work of a psychopath – ‘Who else would do something like this?’ says Pete, 43, with Brandy the spaniel cross. ‘And it’s not a one off.’

Sadly, he’s right.

A dog was poisoned in Hyde Park a couple of years ago. I’m told there was another near Ladbroke Grove. There were reports of poisoned meat in Fulham just last year and in 2019 a dog poisoner was at large in Wimbledon.

It goes without saying that death by poisoning is deeply unpleasant. According to the RSPCA, while symptoms can occur from 30 minutes after a chemical has been ingested, it could take two or three days for signs of kidney failure to occur.

So owners are advised to look out for their pets vomiting, seeming depressed or sleepy, appearing drunk or uncoordinated, or having seizures and difficulty breathing.

Last week, professional dog walker Kris Sikora said he’d heard of poisoned toys left around for dogs and, even worse, razor blades in tennis balls.

It’s horrible to hear. Not just because it’s all so cowardly and cruel. But because we Brits love our dogs so very deeply.

After an hour or so in Brompton Cemetery, I head up to Holland Park which is immaculately maintained and, at one end, backs on to Phillimore Gardens – one of London’s most expensive streets with average house prices at more than £20million. The cafes here are full of dog treats. There’s even a purpose built ‘Dog Toilet’ filled with fresh golden sand for our canine friends to take a quick comfort break.

And the dog owners are astonishingly friendly and chatty. During the course of the day, I speak to a lot of them.

There’s Heeba, whose Japanese akita, Kai, would never touch poisoned meat – ‘He would never dream of scavenging anything – he’s much too clever. He’d know something was wrong.’

And Charlie, an old boy in red trousers at the Holland Park end of the park, who has to watch his golden labrador Maisie like a hawk because ‘she’s basically a dustbin – she’d eat anything’.

And Lauren, who is carrying Wes the westie, because she’s too nervous to put him down.

But perhaps it’s lovely Julie, here with Sophia the blind 15-year-old spaniel, who puts it best. ‘Why would any human being want to do it? I just don’t understand. What motivates you? It just baffles me. I have no words really,’ she says.

It really is bewildering. And also deeply galling that, while deliberately poisoning an animal, including foxes, is a criminal offence under the Animal Welfare Act 2006 and carries a maximum penalty of up to five years in prison and/or an unlimited fine, the likelihood of catching anyone is very low.

‘We have to actually catch someone in the act, which is hard in a park, with limited CCTV and open antisocial hours,’ says a police spokesman, who also confirmed that, while a warning notice was issued, the Met have not opened an inquiry and currently do not intend to.

Which is just too much for some people to deal with.

Such as Rosie, sitting on a park bench by the football pitches with her randy grey pug Chico, who is not on a lead, but does not leave her sight.

‘There are evil people out there who don’t know right from wrong. They need a really good slapping, that’s what I would prescribe.’

Jack, standing nearby with Snoops, a very rotund chihuahua, takes it a step further. ‘The police aren’t going to catch them. They never do. A bit of vigilante action is what’s needed here and one of us dog walkers would do it. I know I would if I caught them – I’d really show them.’

Happily, most dog owners have no interest in violence. They just want their beloved pets to be safe. They watch them like hawks, and keep them close – some on short leads, others in their arms.

‘It doesn’t make any sense and the thought is too awful,’ says Joanna, gazing soppily at her 18-month-old miniature poodle, Kai. ‘Because our dogs are like children, especially when they look at you with their big eyes.’