The work was unveiled in Dublin's Portobello area in 2019 to celebrate the naturalist's 93rd birthday, and received a warm welcome from local residents.

However the group, known as Subset, was taken to court by Dublin City Council for failing to obtain planning permission for the mural, and two others.

Under the Planning and Development Act 2000, artists in Ireland must seek permission from the local authority to create a mural.

"We all say it's so serious that it's a joke," one of Subset's co-founders - who asked to remain anonymous - told Sky News. "It's very difficult, very stressful."

"There's a lot of ramifications, which makes it incredibly difficult for us to pursue our greater vision, and our greater ideal for Irish arts and culture, when we're consistently engaged in legal proceedings."

"All of this makes it incredibly difficult to live day-to-day. The impact it has on the crew, our resources, our time, our energy, it's difficult."

The collective says it only paints murals with the full consent of building owners.

Henry Hopkins, who owns the house with the David Attenborough piece on its gable end, is a fan of their work. He told Sky News that prior to being approached by Subset, the wall was continuously tagged with graffiti, and was "an eyesore". That problem had largely ceased once the mural was painted.

But planning permission had not been sought for the piece, nor for "Horseboy", a mural depicting a boy atop a horse, or Think & Wonder, a piece with a mental health theme that appeared on the gable end of a cafe on Grantham Street. The council issued enforcement warnings to Subset, demanding they remove the murals, but they declined.

"We're not just going to bend the knee and roll over for authority," the group's spokesperson said. "Especially when we feel that the position or the stance that we're taking is one we feel will benefit Irish arts and culture, and Irish society in general."

The collective is demanding new legislation to remove the role of local authorities in the creation of public space art.

They want a model like that found in Sydney, where artists can create a mural with the consent of the building owner, as long as the material is inoffensive.

The spokesperson said that "our ultimate motivation is a change in legislation which will be a catalyst for more creative exploits, more artistic endeavours, and generally speaking an improved society".

For now, the case against Subset is in limbo. Dublin District Court most recently heard that the council wishes to strike out its case, but that Subset's legal team fear this is merely "a tactical move" before the council starts fresh proceedings against the artists in a higher court. The judge in the case has adjourned the matter until September.

In a statement, Dublin City Council told Sky News that it could not comment as "mural cases continue to be the subject of current legal proceedings", and "there are also further legal proceedings being considered relating to murals painted in the public realm within the city".

However, speaking in broad terms, an official said that the council was fully supportive of public art work in appropriate locations, and once approved through the correct channel.

'Public art is incredibly valuable to a society and to a culture'

Dublin City Council had given permission for at least 35 large-scale public art installations in the past year, and had previously commissioned Subset to paint murals in approved locations.

Murals, and other public space art forms, have proliferated in Ireland in recent years.

At the Icon Walk, a public art installation on Dublin's Bedford Lane, there are approved murals and a council-commissioned tile piece hanging overhead.

Eric Conlon from Alternative Dublin runs walking groups, guiding locals and tourists through the capital's many examples of street art. He says murals deter anti-social activity.

"In this laneway, this public art gallery brings people down the lane constantly," Mr Conlon said. "Before, there wouldn't have been many people visiting, but now there are always hundreds of people walking down here. That traffic reduces the issues that would've been found here before."

The Subset spokesperson said: "I think it's pretty widely accepted that public art is incredibly valuable to a society and to a culture. The bone of contention seems to be how that takes shape and how that manifests, and the process by which that happens."

The group says it is losing money, as individuals and companies appear reluctant to hire Subset while legal proceedings continue.

The collective's co-founder is resigned to the situation. "It's just another day," he said. "It's just…bite down on the gumshield, and finish off the fight."