Patriotic drivers showing their support for England with window flags during the World Cup will pay more in fuel costs, an academic has claimed.
The flags create drag which costs an extra pound an hour
An average car with two flags attached burns an extra litre of fuel per hour at an average of 70mph, said Manchester University's Dr Antonio Filippone.
He also calculated that 500,000 drivers all doing the same will create 2.8m kg of carbon dioxide emissions.
The extra fuel consumption is caused by the flags creating drag.
Dr Filippone, of the School of Mechanical, Aerospace and Civil Engineering, carried out the research for a paper called "What is the fuel wastage from the flag on your vehicle?".
He said: "The extra drag generated by these flags can reduce a car's fuel economy by up to 3% during a one-hour journey.
"This may not seem significant to the individual, but if half a million cars are flying these flags we could see up to 1.22 million litres of extra fuel burned during the World Cup."