VW's US boss knew of "possible emissions non-compliance" in 2014

The revelation comes from Volkswagen Group of America chief executive Michael Horn in a written testimony he will present on Thursday to a House Committee investigating the scandal.

He said he was made aware of the issue after a West Virginia University study was published in spring 2014.

"I was informed that EPA regulations included various penalties for non-compliance with the emissions standards and that the agencies can conduct engineering tests which could include 'defeat device' testing or analysis,” he said in his testimony, according to Sky News.

"I was also informed that the company engineers would work with the agencies to resolve the issue.

"Later in 2014, I was informed that the technical teams had a specific plan for remedies to bring the vehicles into compliance and that they were engaged with specific agencies about the process."

Horn also apologised for the German carmaker's "deeply troubling" actions.

"I did not think something like this was possible at the Volkswagen Group," he said.

"We have broken the trust of our customers, dealerships, and employees, as well as the public and regulators."

Sky News reported that Horn said the embattled company takes "full responsibility for our actions and we are working with all relevant authorities in a cooperative way" and that it is "determined to make things right".

The company said 11m diesel engine cars globally are fitted with defeat devices, which reduces carbon emissions from the vehicles when under test conditions to within standards.

In the UK, nearly 1.2m cars are fitted with the software.