In March, 2025, the Shared Data Unit reported how thousands of parcels of potentially contaminated land, which have never been checked by local councils, could be posing a risk to health and even life.
The collaboration with BBC Wales Investigates found only one-in-ten potentially âhigh riskâ contamination sites in Great Britain have been properly inspected in the 25 years since a law was introduced to fix the toxic leftovers from the days of heavy industry.
Those sites include former tips, tar pits and military facilities among many others.
However, the lack of so-called âintrusiveâ studies, such as soil tests, could be leaving thousands of households at risk from serious contaminants including lead, arsenic and asbestos, some experts say.

The Department for the Environment, Farming and Rural Affairs (Defra) said it had commissioned a new report to look into the state of contaminated land across the country.
Phil Hartley, a former environmental officer previously in charge of fixing Newcastleâs contaminated land, said the findings did not come as a surprise.
âI think if there is no funding from central government, councils are reluctant to go out and find sites,â he said.
âIf they find itâs a contaminated site where there is a possible risk of harm there will be substantial costs involved and they donât want that.
âThereâs a risk to health there and thatâs not good.â
The BBC study found at least a dozen councils across Britain had not carried out any inspections on their highest risk sites since the year 2000. Others simply had no centralised record as to how many of their sites had been tested.
In the year 2000, councils in England, Scotland and Wales were ordered to draw up a list of potentially contaminated sites in their area and remediate - or fix - those considered a genuine risk to human health.
To find out how effective the legislation has been since then, the BBC obtained Freedom of Information requests from 122 of the biggest unitary councils across Great Britain.
We received a full response from 73 of those authorities. They initially discovered a combined 430,000 potential sites during their âdesktopâ research back at the turn of the century. This involved reviewing the historical land use of sites in each area and any possible contaminants that might be present, but did not involve any form of physical testing.
Only around 13,000, or 3% of those sites, were thought to be potentially âhighâ risk or âhigh consequenceâ.
But the BBC study found just 11% of those âhigh riskâ sites have ever had an intrusive inspection.
The details from those FOIs include:
- Details of the number of âsitesâ first considered to be a potential risk of contamination at local authorities.
- The number of sites considered to be âhigh-riskâ
- The number of sites to receive an intrusive inspection
- The number of sites that have not been remediated despite being a âconsiderable riskâ to health
Although councils in Northern Ireland have never drawn up a high-risk register (see background in the story pack) we can share with you how many sites were identified as being a potential risk at each local authority area in the country.
Get the Data here And the story pack here
The story featured as an iPlayer documentary Britain's Toxic Secret, which appeared on BBC Wales on 13 March. It was also developed into an online story read by more than 640,000 people.
The piece was used on bulletins across the BBC's national and regional network and a television package feature on Breakfast on the morning of Saturday, 15 March.~
Partner usage from our wider partner network included:
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Nation Cymru: BBC investigation reveals âtoxic secretâ beneath our feet, 13 March, 2025.
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Aberdare Online: Nine out of 10 âhigh-riskâ toxic sites have not been tested by councils, BBC investigation finds, 13 March, 2025.
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STV: At least 5,000 most high-risk toxic sites untested by Scottish councils, 14 March, 2025.
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Daily Record: Two 'toxic' sites in West Lothian among national list of untreated contaminated land, 14 March, 2025.
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Wales Online: "Unchecked 'toxic' land may have left Welsh star's child 'seriously ill', 14 March, 2025.