Ms Anderson, who is seven months pregnant, said: 'The bikes have changed our lives and the children love it. We have a cover for when it rains, and while I might get wet, the children are cosy. I've used it for grocery shopping, getting to after-school activities, trips to the park and even to the recycling bank with a load of cardboard and bottles. It can be quite tough but you do save on gym membership. 'It's the ultimate eco-friendly people carrier.' The popularity of the machines is likely to have been boosted by Richmond raising the cost of a parking permit for a large-engined "gas guzzler" to £150. It is also considering charging £75 for an annual permit to drop children off at school by car.

Tony Juniper, director of Friends of the Earth, said he had bought his wife a cargo bike for Christmas: 'We've been trying to cut down on car use and this is perfect for shopping and carrying heavier goods. We even take our youngest to chess matches.' A spokesman for the Royal Society for the Prevention of Accidents said cargo bikes looked no more dangerous than other bicycles, but added: 'It will handle differently from a normal one so people should get training or practice first in a safe environment.'