Laboratory tests have shown that compared to ordinary diesel, City Diesel reduces particulate measures by up to 84%, reduces hydrocarbons by 50%, carbon monoxide by 35%, sulphur dioxide by 98.5% and nitrous oxides by 13%.

Robert Constant, group transport manager of London Electricity, which runs around 1,000 diesel vans and 70 diesel cars, said the policy will cost London Electricity two pence per litre above ordinary diesel prices, but said the price was worth paying. Sainsbury is currently the only UK retail stockist of City Diesel, and Constant believes its network is adequate for the operational area of his fleet.

Roger Vaughan, project officer at Westminster City Council, said the authority's decision to switch to ultra low sulphur City Diesel would affect around 60 vehicles, typically buses run by the education department and social services.