A new 10-part series from BBC Radio 4 investigating the secret dumping of an estimated million tonnes of waste – some of it now highly toxic – near a drinking water supply in Northern Ireland, has revealed officials may have broken the law in their handling of it.

Journalists and presenters Dan Ashby and Lucy Taylor, who specialise in investigating environmental and organised crime, began looking into the story following a deathbed tape from a trucker who was involved in carrying waste to a site in Mobuoy Road, near Londonderry. Heard publicly for the first time on Buried, Joe Ferguson claims that asbestos was seen at the site and trucks came from across the country day and night, for years.

For 10 years it has not been possible to fully report on the story of the Mobouy dump due to ongoing court proceedings, which finally resulted in two men being convicted last year for their involvement in one of the largest illegal waste sites in Europe. The audacious scam involved councils from across Northern Ireland paying criminals to illegally dump families' recycling - for years on end - in a special area of conservation.

Now the BBC has seen a key 'missing memo' that reveals that civil servants and officials in the Northern Ireland Government knew that they had likely broken the law in their handling of the site where the crime took place. This has never been acknowledged publicly and the memo later went missing from an official Freedom of Information act request, prompting campaigners to accuse the Department of 'cover up'.

The BBC has also been given a summary of a secret official investigation into the Government's failures, which found that Northern Ireland's Department of Environment oversaw more than a decade of maladministration - in eight separate areas of responsibility. The Department was so dysfunctional that the people paid to protect the environment repeatedly failed to call in enforcement or do further checks, meaning they lost the power to shut it down.

As the series unfolds, Dan and Lucy go on to examine the impact of waste crime more broadly. The duo travel to Naples to explore the lasting impacts of dumps there on local communities, with fears of toxicity levels damaging rivers, land and even people’s health.

Buried goes on to investigate the full scale of waste crime in the UK, following intelligence from a top satellite waste investigator, suggesting that the Mobuoy dump is part of a wider trend of illegal waste dumping across the UK, with evidence of up to 12 illegal dumps in one national park alone.

With official estimates now suggesting that nearly a fifth of English waste alone is now handled by criminals, could the UK be the home of a new mafia, getting rich from our waste? In this revelatory series, Buried takes a deep dive into a criminal underworld, all the time following clues left in a deathbed tape.

Lucy Taylor said: "Everything about this crime has shocked us, from its scale to the years of silence around it. And we found that although we started by looking at this one example of illegal dumping, the more we learnt about the wider trend, the more we realised that the same thing is happening across the UK. One interviewee, a waste crime investigator, told us that he can't go on a motorway or on a train without seeing signs of an illegal dump somewhere on his journey. And now that we know what to look for, we're starting to notice them too.

"Dan and I have spent years working overseas reporting on environment crimes from Tanzania to Russia, from the illegal ivory trade to dynamite fishing gangs - but this one comes right to our doorstep."

Dan Ashby said: “Your dustbin is like a dark narnia. But no lovely adventure awaits. Instead, if you begin to try to untangle it, it’s more like falling into an underworld.

“I have to walk around and pinch myself - a fifth of English waste alone is estimated to be handled by criminals. Thirty-four million tonnes. Imagine if crooks ran one in five coffee shops, and you didn’t know if the coffee was safe. I can’t quite believe this is normality.”

“We know there are hundreds of illegal dumps in the UK. We know waste crime is a one-billion pound industry. We know they are smuggling guns and drugs. We know toxic dumps are threatening families. The only thing we don’t yet understand is how awful the cost will be to the planet.”

“We can pretend all this is buried, but it’s not - it’s coming back to bite us.”

The Department of Infrastructure in Northern Ireland responded by saying they have no record of the so-called ‘missing memo’, but that since the crime happened, they have focused on strengthening implementation of environmental checks and regulations - including training more than 200 planning officers to improve their competence when dealing with unauthorised developments. They say they accepted the Ombudsman’s findings and have implemented the advised changes, and also stressed that eventual enforcement action from officials did help shut down the site. The Department of Agriculture, Environment and Rural Affairs (Northern Ireland) went on to say they have increased their testing of the drinking water supply at the River Faughan, and to date, no adverse impacts on tap water attributable to the dump have been detected, but they acknowledge "there is no room for complacency” - and if the need arose, they would stop using the water supply near the dump.

Buried is available on BBC Sounds first as a box set from yesterday (23 January), and broadcast weekdays on BBC Radio 4 at 13:45 from yesterday (23 January).

Buried was written and produced by Dan Ashby and Lucy Taylor from Smoke Trail Productions, for BBC Radio 4.