The organisation has stopped the practice in case girls damage the vehicles, opening up the 550,000-strong organisation to compensation claims.
Guides are also banned from bungee jumping, paint-balling and laser games. However, Scouts are encouraged to do all of these activities – especially washing cars.
In fact, they say they're even attracting more girls to the movement because it's more exciting!
The Girlguiding website states that the banned activities are deemed to be either too dangerous or go against the spirit of the organisation.
Under a section headed Car Washing: Prohibited Activity, it says the ban is 'due to the insurance implications to Girlguiding regarding the possible damage to vehicles.'
Girlguiding spokesman Kim Sanders said: "We don't allow car washing for purely insurance reasons. Thousands of girls and women take part in a variety of activities in Guiding safely every year."
The differences between Guides and Scouts has sparked a mini battle of the sexes.
TV presenter Sue Cook told the Mail: "I'm amazed to hear that car washing is prohibited for Guides. I can't think what the rationale for that can be in this day and age.
"My daughter earned money in the school holidays as a young teenager by car washing.
"If it's OK for the boys, how can it not be OK for the girls?"
Scout leader Chris Foster, who works in North London, said: "Car washing is one of our main fundraising events and will help pay for us to go to the Scout jamboree in Japan next year.
"We identify activities that young people want to do and whether it is appropriate to do them.
"It's a case of learning life qualities. We might get the Cub Scouts to do the wheels and tyres, as that's what they can reach and do safely. The older Scouts would do the bodywork because they are able to focus more and are taller.
"Our organisation is becoming very popular with girls because of all the exciting activities we do."
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