Around 1.6 million motorists are taking legal action against more than a dozen manufacturers over claims that several diesel vehicles made from 2009 onwards contained "prohibited defeat devices" (PDDs) that allowed them to cheat emissions tests.

The manufacturers are resisting the claims.

Campaigner Rosamund Adoo-Kissi-Debrah gave her support to the case outside the Royal Courts of Justice in London ahead of the start of the trial on Monday.

Her daughter Ella Adoo-Kissi-Debrah, a nine-year-old from south-east London, suffered a fatal asthma attack in February 2013 after being exposed to excessive air pollution.

On Monday, Ms Adoo-Kissi-Debrah told the PA news agency that around 250,000 children in London have asthma.

She continued: "I'm here to raise awareness about the impact diesel is having even now on young people's lungs.

"I am hoping the day of reckoning will be coming.

"In America and Germany I feel they've had some sort of justice, here there's been absolutely nothing at all."

Ms Adoo-Kissi-Debrah said she would like an apology from the Labour Government, saying drivers were encouraged to buy diesel under the government led by former prime minster Sir Tony Blair.

She continued: "To all the young children as it gets colder who will be rushed to A&E, I can only apologise.

"One day soon, hopefully diesel will no longer be on our roads."

In a landmark coroner's case in 2020, Ella - who had lived 25 metres from the busy South Circular Road in Lewisham - became the first person to have air pollution listed as a cause of death at an inquest in the UK.

On Monday, Ms Adoo-Kissi-Debrah called for change, adding that there has been "very little action" since her daughter's inquest, and asked Health Secretary Wes Streeting "to really put a rocket up his Government to do something about diesel".

Also attending the first day of the trial was Adam Kamenetzky, 45, who bought a Mercedes SUV in 2018 "on the premise that it was a clean and green" vehicle.

He told PA: "On the website, it clearly showed that the emissions figures for these cars were top of their class.

"You're paying a premium for all these emissions regulation systems that are there to drop the emissions to well within Euro 6 legal levels. On the basis of the evidence I've seen going to this trial, that's a lie."

He added: "Millions of them are due compensation, but that could take years to materialise, and based on the evidence being submitted today, I feel there's a need for public, if not criminal, inquiries, if these allegations are borne out, to hold these car manufacturers to account."

The claim is the largest of its kind in English history, with the High Court previously told it is believed to be worth at least £6 billion.

Those taking legal action either bought, leased or otherwise acquired a diesel vehicle made by one of the companies, with most living in England and Wales but some living elsewhere in the UK.

They claim that the PDDs installed in the cars allowed them to detect when they were being tested and alter the amount of harmful emissions produced, allowing them to pass.

Law firm Leigh Day, which represents some of the motorists in the case, said that while the main trial is due to conclude before Christmas, legal arguments will not be heard until March 2026.

A ruling is then expected next summer, with a further trial to determine any compensation scheduled for autumn 2026.

Mother hopes for 'day of reckoning' after daughter's pollution-linked death