The right primary school for three-year-old Ranjan should have been an obvious choice. His grandparents live a short walk from the nearest one, on their road in Southall, west London, and enrolling him there would make life easy for the family. But they are so worried about the “petrol-like” odour from a nearby building site that in September Ranjan will travel to a school more than two miles away.

“He has been so sick for the past year – coughing and with a runny nose – that we worry being near the smell all day would make him ill,” said Ajaib Flora, his grandfather.

From an upstairs window at their house in Beaconsfield Road, the family can see the edge of the 88-acre former gasworks that is being redeveloped by St James for the Berkeley Group for 3,750 homes and up to 500,000 square feet of commercial space next to the Crossrail route into central London. They have also been able to see a vast bank of soil a few metres from their back garden on the site of the Southall Waterside development.

In early 2017, work began on cleaning the soil on the site, using a process (remediation) to remove contaminants in an open-air “soil hospital” (that bank) behind the homes. The soil was found to contain hydrocarbons including benzene, a known carcinogen, naphthalene, asbestos and cyanide, and it was decided cleaning the soil was safer than transporting contaminated material along residential streets.

Ealing council said the first phase of cleaning had now been completed, but it was not clear when and how further remediation would take place.

For two years, residents have been complaining to Labour-run Ealing council and Labour MP Virenda Sharma that the odour from the site is making their lives a misery and making them ill. On five visits to the area, it was easy to detect the tarry smell, whose intensity depends on weather conditions.

This mess is at the back of my house, asbestos is in my body, and my children are suffering Resident Joe Bhanghu

In March, Southall Labour party passed a motion of no confidence in Sharma, raising, among other issues, his response to concerns about the site. “This mess is at the back of my house, asbestos is in my body, my children are suffering and you [Sharma] haven’t even come to meet us,” said Joe Bhangu, who lives on Beaconsfield Road. After initially speaking out in 2013 against the 25-year project to redevelop the gasworks, Sharma had changed his mind.

Bhangu was among 50 residents interviewed by the Observer who said their own or their family’s health had deteriorated over the past two years. They spoke of breathing difficulties, the onset and worsening of asthma, eye irritation, irregular heartbeats, migraines, skin rashes, chest infections, nausea, dizziness, memory problems, a sensation of “internal burning” and other symptoms. Some said they only felt well out of Southall. The elderly deterred young relatives from visiting.

One, Amrik Mahi, on Greenland Crescent, said: “First, I didn’t know what was happening. I used to walk two or three miles a day and suddenly I couldn’t go more than 100 yards without feeling as if my chest was exploding, on fire. The GP diagnosed asthma and gave me inhalers but I can hardly get to the end of the road.” Janet Griffiths, who lives on Tilney Road, often has a sore throat. A few months ago she had an eye ulcer. Then her GP diagnosed an enlarged heart. David Marsden, of Savera Close, said frequent chest infections had kept him off work. His neighbour Angela Fonso reported an “internal burning sensation”, sore throat and memory problems. “I feel like my neighbourhood is killing me and no one is listening.”

Facebook Twitter Pinterest Angela Fonso, with daughters Emma, right, and Karen, says she suffers from memory problems.

Speaking anonymously, parents of pupils at Blair Peach primary school – on the edge of the site and near Ranjan’s grandparents’ house – said the odour was affecting their children’s health. “About two years ago when my son started in reception there was a really strong chemical smell. At first we thought it was a terrorist attack at Heathrow,” said one. “All through year one his classroom window was about 10 yards from the site. He had a permanent blocked nose.”

The minutes from a Blair Peach governors’ meeting on 29 November 2017 record that head teacher Anita Puri had “noted that a chemical odour from the site from the building works had been extremely strong, resulting in headaches and asthma attacks”, and that the Environment Agency (EA) would report back once its investigation was complete. The same minutes record that Berkeley’s site construction manager, Richard Watler, had been appointed a co-opted school governor. Puri declined to be interviewed for this article.

Some residents now plan to leave Southall despite not wanting to leave extended families. Their residents’ main anxiety is about the long-term health impact of the “petrol-like” odour. They want their health and the air inside their homes to be tested.

Southall Waterside is one of the most audacious brownfield developments under way in the UK, where councils have new tools to speed up development of derelict land as part of a national plan for housing.

The experience of Southall residents suggests the measurement possible health impacts of brownfield sites needs an urgent review. It also raises questions about how housing developers are permitted to encroach on areas such as education, highlighting potential conflicts of interest in an era when councils prioritise housing quotas.

Built in 1869, the “old gasworks” was a large, bleak triangle of land on the edge of Southall, home to the UK’s largest Sikh population, where more than half the population are south Asian. The site also once hosted a chemicals factory.

Facebook Twitter Pinterest Blair Peach primary school, on the edge of the site: parents say the tarry smell has affected their health.

“It was like Mordor, completely dead. Nothing grew there and Southall grew up organically around it,” said Oliver New, who lived in a converted water tower next to the site and led earlier campaigns that helped persuade Ealing councillors that development would put too much pressure on local infrastructure and that the soil was too contaminated to be safe.

A toxicology report obtained via a freedom of information request contains the line: “There are no private gardens proposed cannot grow vegtables on the contaminated soil ever! [sic]”

New said: “Alarm bells rang on and off from 2005 until 2010 with developers eyeing the site, but both Labour and Tory councils backed off.”

But in September 2010, then London mayor Boris Johnson overruled the council’s decision against site development, using special powers to give the go-ahead for a project that would bring more than 600 jobs to the area and paving the way for National Grid to sell the land.

Because of its scale, the gasworks redevelopment has multiple regulators: it is up to the EA to regulate the soil and advise Ealing on management of land affected by contamination; Ealing has responsibility for investigating complaints of statutory nuisance; and Public Health England (PHE) and Public Health Ealing are supposed to protect the health of the public. Despite residents’ complaints to the council and other bodies, none has taken action on the odour that is making them sick.

Ealing called in the EA, which told Berkeley to put in place a more extensive odour control scheme, which the developer complied with, and asked PHE to review the available air quality monitoring data, provided by the Atkins consultancy on behalf of Berkeley Thames West. Using this data, PHE concluded the risks to health were minimal. Its interim review said: “On the basis of the available monitoring data, average levels of VOCs [volatile organic compounds] have been below or comparable to guideline or assessment levels.”

However, Ealing has never ordered independent air quality monitoring to compare with Atkins’ data.

Dr Onkar Sahota, an Ealing GP and member of the Greater London Assembly (GLA), said: “I was astonished that Ealing council does not undertake their own monitoring – they have an obligation to defend the interests of their residents so why have they delegated this to the developers?”

He is also surprised that PHE was prepared to leave the matter to the council and not take further steps, such as alerting Southall GPs to possible health impacts of the redevelopment.

Facebook Twitter Pinterest The site in 2008 before it was cleared for development. Photograph: Alamy

A PHE spokeswoman said: “Quality assurance is the remit of the relevant regulator [either the EA or local authority], who are responsible for approving the monitoring strategy.” She went on: “I can confirm, however, that PHE did not have concerns in this case when we were asked to review the data by Ealing.”

Julian Bell, leader of Ealing council, said: “It is standard practice for the company that is doing the works to collect the air quality monitoring data. It would not make sense to replicate the monitoring that Atkins is doing, not to mention the cost this would incur. We aren’t the primary regulator – the EA are – and they say clearly there is no further action that needs to be taken. And although this is a nuisance in terms of smell, human health is not impacted.”

PHE recently updated its report, saying that levels of naphthalene needed to be urgently reduced.

“It would be undesirable for the levels of naphthalene on site to remain elevated and the levels should be reduced to prevent prolonged exposure,” it said.

Alastair Lewis, a professor of atmospheric chemistry at York University, said one problem is that the system for measuring VOCs tends to use measures based on occupational hazards rather than those that might be applicable to residents.

“More needs to be done to take seriously the adverse effects reported by a small fraction of the population to VOC exposure, and that recourse to comparison with workplace standards for air quality is inappropriate given that those individuals have little choice over their exposure,” he said.

Sahota, the Ealing GP, said: “We are facing a major health challenge as more and more homes are built on brownfield sites and we don’t yet know the impact on health.” He refers to a development by Telford Homes in Hackney, east London, which was forced to shut after residents complained of ill-health.

Campaigners against the Westbury estate development in Lambeth claim the Labour council has ignored the complaints they are exposed to asbestos. After publication, a spokesman for Lambeth council challenged the claim. A council statement said that asbestos removal work at the estate had been carried out in line with national regulations and standards, and that the council had taken seriously all queries over the Westbury development and written to and visited residents who had raised concerns.

It has not helped that while in Ealing there are currently five monitoring stations to measure general air quality, there are none in Southall, which is undergoing intense regeneration. There used to be three such stations in Southall, but they have been shut down. One outside the Blair Peach school was removed in June 2016. Ealing said in an email seen by the Observer that the monitoring stations had reached the end of their life span.

Southall is one of Britain’s most deprived areas: life expectancy for men here is six years less than in nearby Hanger Hill. English is often not the first language and cultural barriers prevent people from speaking out, said Sahota. It is the kind of community that finds it hard to fight back, he said. “Because this is a deprived community, they need a more powerful and more intrusive council to act on their behalf.”

The total value of Berkeley’s construction projects in Ealing is estimated to be £1bn.

There is no doubt that regeneration of the old gasworks will eventually revitalise Southall, bringing new homes, jobs, shops and leisure space.

But for residents such as Mahi it is coming at a very high price. “They think because we are Asian, we will keep our heads down and won’t complain. They think we are expendable.”

A Berkeley spokesperson said: “This is a highly regulated activity and all work has been closely monitored and approved by the authorities, including the London Borough of Ealing and the Environment Agency. Cleaning this land has brought it into use for much-needed housing.”

• This article was amended on 7 and 8 May 2019: to express an estimate in square feet instead of square metres; and to add comments by Lambeth council.