RSPCA investigators have taken photographs in the garden of the lawyer Jolyon Maugham QC as part of an animal cruelty investigation after he clubbed a fox to death with a baseball bat while wearing a kimono, the Guardian understands.

The investigators visited Maugham’s London home on Thursday night as the debate continued over the remain supporter’s justification for his actions, which he revealed in a Boxing Day tweet that received 10,500 replies and widespread media coverage.

Animal welfare workers expressed sadness at Maugham’s killing of the fox, which they said was needless.

“It is absolutely shocking that this wild animal was condemned to such a brutal death,” said Isobel Hutchinson, the director of Animal Aid. “It is deeply saddening that anyone should react in this way when coming face to face with a wild animal.”

According to tweets and interviews, Maugham woke up on Thursday morning to the sound of a commotion in his back garden. Still nursing a hangover, he pulled on the first garment he could find – his wife’s green satin kimono – armed himself with a baseball bat and walked out of the back door.

The fox was trapped in the netting surrounding Maugham’s hen house. He has said his violent response was at least in part triggered by the grief of losing chickens to foxes in the past.

Maugham tweeted: “No one should relish killing animals – and I certainly didn’t … Many or most councils in London treat foxes as an urban pest. And at least one recommends clubbing them. To those concerned I have broken the law, I called and spoke to the RSPCA and left my contact details.”

Terry Woods, a wildlife consultant with Fox-A-Gon, which helps individuals and businesses with humane fox deterrence, suggested Maugham may have committed an offence under the 1996 Wild Mammals (Protection) Act.

The law makes it an offence for anyone to mutilate, kick, beat, nail or otherwise impale, stab, burn, stone, crush, drown, drag or asphyxiate any wild mammal with intent to inflict unnecessary suffering.

“He should have done what any reasonable person would’ve done, which is call the RSPCA,” Woods said. “Had I turned up, I would have covered its head so it couldn’t see, which quietens them down considerably, and cut the mesh.

“I would then, as someone who deals with this all the time, [have] taken it to the vet to see what injuries it had suffered.”

Woods said it was not uncommon for foxes to become trapped in netting of the kind used in children’s football goals or to keep birds away from growing fruit, but it should not usually be possible for one to become trapped in a chicken coop.

Any coop that poses a risk to foxes also poses a risk to the hens it is supposed to protect, said Tara Kenward, who kept chickens for a decade in south-east London.

While fox numbers in London are believed to be stable, according to data collected by the British Trust for Ornithology, the population of the red fox has fallen by 42% across the UK in the past two decades.

While a number of scare stories have circulated in recent years about urban foxes, including that they spread diseases such as mange and have attacked pets and even small children, some experts say they are beneficial.

Woods said: “We should learn to live with the urban fox. If you take the fox out of the equation then you are overrun with other things that you don’t want. If you’ve got foxes, you are not going to have rats, for example.

“Their natural food intake would be a mixture of rodents – mice, rats, voles. When we go underneath houses, we find a lot of squirrel remains. Funnily enough, with rats they appear to kill them but they don’t eat them.”

The RSPCA would not comment further on the investigation.