Almost every new Mercedes-Benz diesel car bought in the UK during the past six years is being voluntarily recalled to improve their emissions performance.
German firm Daimler, which makes the vehicles, said the measure to reduce nitrogen oxide (NOx) output will involve no cost to owners.
The action is being taken in relation to nearly all cars with diesel engines meeting the Euro 5 standard - implemented in 2011 - and the existing Euro 6 rules.
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The firm would not confirm how many UK owners are affected, but said one million vehicles in Germany and two million in the rest of Europe are being voluntarily recalled.
Some 170,000 new Mercedes-Benz cars were registered in the UK last year alone.
Diesel emissions have come under huge scrutiny since Volkswagen Group admitted in September 2015 that 482,000 of its vehicles in the US were fitted with defeat device software to switch engines to a cleaner mode when undergoing environmental tests.
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The German manufacturer said 11 million of its vehicles were affected worldwide - including almost 1.2 million in the UK.
A Government report published in April 2016 showed diesel cars being sold in the UK emit an average of six times more NOx in real-world driving than the legal limit used in official tests.
Dr Dieter Zetsche, chairman of the board of management of Daimler AG and head of Mercedes-Benz Cars, said: “The public debate about diesel engines is creating uncertainty - especially for our customers.
“We have therefore decided on additional measures to reassure drivers of diesel cars and to strengthen confidence in diesel technology.
“We are convinced that diesel engines will continue to be a fixed element of the drive-system mix, not least due to their low CO2 emissions.”
The company said the voluntary recall will cost it around 220 million euros (£195 million).