London mayor Ken Livingstone is planning to push ahead with a £5 congestion charge next year in a bid to cut traffic levels by 15%. But analysis by the rental firm has suggested more cars could end up on the streets because the rules do nothing to encourage people to rent rather than buy.
Rental companies campaigned vigorously to be exempted from the charge, but their pleas were ignored.
Brian Jayes, operations director for National Car Rental, said: 'We believe city congestion charging will have a negative impact on the residents of London.
'City dwellers use rental for weekend and business trips, eliminating the costs of vehicle ownership and the problem of parking when the car is not needed. The new rules do nothing to encourage people to rent instead of buy. Indeed, residents using a rental car for less than five days will not receive a discount on the congestion charge and will have to pay £10 to register.
'Furthermore, there is no ability to see if a car has a congestion charge payment made. This could potentially cause confusion for both rental companies and their customers.'
National believes congestion charging may force rental companies to close in the affected zone because of the reluctance of customers to pay the fees, which could account for a significant increase in the cost of hiring a car.
There is also no reduction for non-revenue movements of vehicles within the charging zone between hire stations.
Jayes added: 'If rental locations close, jobs will be lost and residents will be forced to consider buying a vehicle, because they will no longer be able to rent. Given these factors, it is hard to see how this could be regarded as a green initiative. We sincerely hope that exemption on car rental will be reconsidered before the scheme is introduced.'