Both Lewis and WWF have some Valid Points
WWF clearly is writing extremist and irrational stuff, so Lewis is right about that. But certainly the world cannot go on with the Western Model Of Resource Consumption.
Especially Automotive Mobility in the West is at a crazy level. America consumes about 25% of the world crude oil supply just that they can move their often obese bodies comfortably from home to work and back every day. With them, they often move a 1.8 ton "SUV" vehicle. That kind of activity clearly cannot be perpetuated, as oil production cannot be increased to fuel the same activity in China and India.
There are many possibilities of reducing that activity drastically without the dystopic visions of Mr Page being implemented. Buses and trains do not have to be smelly and cramped. British incompetence does not mean it is generally impossible to have decent train and bus services. Also, novel approaches such as dynamically scheduling buses, taxis trains requested by mobile phone could greatly improve service quality and reduce waste.
Also, Western Meat Consumption Habits are both unhealthy and impossible to scale to China, India and Africa. One Joule of energy from meat requires at least six Joules of energy from grain, maize etc to feed the livestock which is used for the meat. We can already see that food prices appreciate sharply in the western world, because the Chinese have increased meat consumption. Also, eating so much meat is definitely not healthy. So if they would put it more moderately, the WWF would have a point.
In general, I do think there can be further "growth", but probably not in energy and meat consumption or the number of human beings. China's population control measures should be applied to Africa and Asia in general, if we want to avoid very serious problems. Development aid should be Distributing Condoms, not distributing wheat sacks.
"Growth" can indeed be realized in many, many fields such as software, mobile phones, internet services, teleworking, telepresence, eco-friendly technologies such as water treatment plants, home insulation. "Growth" is not necessarily related to buring more fuel or driving more miles.
Humanity is already living in a quite crowded planet and constantly building more roads, parking lots, airports and houses does not make me happy. But that does not mean I am advocating the return to stone age. There are so many ways to reduce resource consumption without selecting the extremist visions. For example, we could travel by train to Spain from Northern Europe, which could be done by using CO2-friendly train travel powered by nuclear power, thereby saving on fuel-hungry plane travel.
I sometimes think Mr Page is a British Petroleum $hill. After all, selling pertroleum is one of Britains biggest industries...