Residents are preparing a legal challenge to the redevelopment of a former gasworks in Southall, west London. The move follows two years of complaints to Ealing council, developers the Berkeley Group and environmental regulators that a petrol-like odour from the site is making them ill and putting children’s lives at risk.

“The campaign group has become increasingly frustrated by the abject failure of Berkeley adequately to respond to legitimate grievances,” said Jo Sidhu QC. “We now have no choice but to instigate legal action to hold them accountable for the damage they have done to the health of local residents. People are suffering serious and chronic illnesses relating to the toxic pollution released by the land being used by the developers.”

He added: “This is an immediate and urgent public health crisis and we are determined to pursue every legal route to stop the building works and to seek substantial compensation for injury to those who continue to suffer.

“Public nuisance is both a criminal offence and a civil action in tort. It also involves substantial breaches of environmental law.”

Sidhu, who grew up in Southall, said that in preparation for legal proceedings campaigners who lived near the site were collecting data on respiratory problems, chest pains and other symptoms reported since work began on the Southall Waterside development in early 2017. The Observer has spoken to 50 residents who said their health had deteriorated since then. Soil on the 35-hectare site was found to contain hydrocarbons including benzene, a known carcinogen, and naphthalene, as well as asbestos and cyanide.

Dr Onkar Sahota, a local GP and a member of the London assembly, said he had heard from many residents that their asthma and other symptoms had worsened since “being exposed to the offensive smell and debris in the air”, and that he was pressing Ealing council to gather health impact data.

The site has multiple regulators: it is up to the Environment Agency to regulate the soil and advise Ealing council on management of land affected by contamination; the council is also responsible for investigating complaints of statutory nuisance; and Public Health England (PHE) and Public Health Ealing are tasked with protecting the health of the public.

A PHE spokesperson said: “It would be difficult to establish that any health effects to the nearby population are due to the site works rather than other underlying factors. It is therefore considered that the most appropriate action is mitigating release of airborne chemicals at source, as recommended in the PHE report.”

The PHE interim assessment of the available air quality data monitoring provided by the Atkins consultancy, hired by Berkeley, found the results for the air quality monitoring are “considered unlikely to pose a direct toxicological risk to the health of the nearby population”, but said levels of naphthalene on site “should urgently be reduced to prevent prolonged exposures”.

On Wednesday residents will put their concerns to the Environment Agency, Ealing council, Berkeley and PHE at a public meeting. “We will demand that there is independent air quality monitoring of the site and steps to reduce naphthalene levels,” said Angela Fonso, from the local campaign group. She said they would also demand the removal of a Berkeley site construction manager as governor at a primary school on the edge of the site.

Facebook Twitter Pinterest Angela Fonso with her daughters Emma, in pink and Karen, in black. Photograph: Antonio Olmos/The Observer

A spokesperson for Berkeley said: “This is a highly regulated activity and all work has been closely monitored by the authorities including Ealing council and the Environment Agency. Any legal challenge will be vigorously opposed.”

Controversy has dogged Southall Waterside, one of the most ambitious brownfield developments under way in the UK, since Boris Johnson as mayor of London in 2010 overturned Ealing’s refusal to grant planning permission, and allowed Berkeley to build 3,750 homes on the site, which is near the Grand Union Canal.

Sidhu attended the hearing after Berkeley appealed. He presented findings to show potential damage to health: “Yet the then mayor simply smirked throughout the hearing with barely an acknowledgement of the seriousness of the situation.”