Politicians used to promise the Earth. Now they promise to save the Earth. David Cameron is the undisputed leader of this new school, as he single-mindedly targets the soft Liberal Democrat vote with one symbolic act of environmentalist concern after another.
Last week it was a trip to the allegedly disappearing Arctic, where the Conservative leader posed with a pack of huskies, cunningly appealing both to dog-lovers and eco-warriors. This week he has declared, "I am swapping my government car for a hybrid with substantially lower emissions."
To be strictly accurate, what Mr Cameron is doing is swapping one government-supplied car - a Vauxhall Omega - for another government-supplied car, a Lexus GS 450H. The H, it is true, stands for hybrid: at speeds of up to around 20mph the Lexus runs off its electric engine: its petrol engine kicks in only at higher speeds. But in other respects the Lexus is, as one motoring columnist puts it, "a scary-fast luxury sports sedan" which can roar from 0-60mph in 5.5 seconds and reach a top speed of 155mph. New British cars on the road currently emit on average about 174 grammes of CO2 per kilometre. Mr Cameron declared yesterday that he wanted that figure to drop to 100 grammes per kilometre. His brand new £38,000 Lexus emits, even according to its proud manufacturers, an average of 186 grammes of CO2 per kilometre.
Not surprisingly, the Labour Party has been quick to mock Mr Cameron's claims of ecological correctness, pointing out that he had turned down the offer of a Toyota Prius, a much less beefy hybrid, with a top speed of only 105 mph, which emits just 104 grammes of CO2 per kilometre. Cameron shot back that "when I go on tour I have a lot of people in the car with me" and that he would need two Priuses - or should that be Prii? - in the place of one Lexus hybrid.
The peculiar thing is that Mr Cameron's predecessor as Tory leader, Michael Howard, has been driving a Toyota Prius for well over a year now. And unlike Mr Cameron, who has been given a new hybrid vehicle out of the public purse, Mr Howard actually bought his Prius secondhand with his own money - £16,000 of it. Mr Howard, however, has an old-fashioned politician's aversion to the flaunting of personal virtue. It would never have crossed his mind that more people might think of voting Conservative if he told them he'd swapped his make of car from gas-guzzler to souped-up milk float.
Sir Menzies Campbell, the leader of the Liberal Democrats, is also an old-fashioned politician. So he has had to be bullied by his young advisers - terrified as they no doubt are by Mr Cameron's advance on their territory - to ditch his much-loved 20-year-old 5.3 litre metallic blue Jaguar Sovereign. The old boy admitted to being "tear-stained" as he sent the big beauty off to the secondhand car salesman.
At the risk of making Sir Menzies feel even more wretched, I should like to know why the Jaguar is to be sold, rather than just kept on bricks, as many cars were during the petrol rationing of the Second World War. By all accounts, Sir Menzies hardly drove the car at all - it seems to have spent most of its time in an East Lothian barn, where he could go to stroke it lovingly. Now however, it will doubtless end up in the hands of some nostalgic boy racer, regularly sending 5.3 litres' worth of petrol fumes hurtling into the atmosphere.
I have a similar question for Mr Gregory Barker, the Conservative shadow environment spokesman who escorted David Cameron on last week's trip to the glaciers. Mr Barker, who happens to be my local MP, last weekend told The Sunday Times that he has just taken delivery of a hybrid four wheel-drive, and that his new car "symbolises the Tories' new approach to the environment." Mr Barker went on: "I sold my Porsche Boxster and bought this instead. It saves me £2,000 a year in congestion charges [hybrids are exempt] and makes me feel virtuous. You can have a better quality of life and save the planet."
(However fatuous you might think those remarks to be, you should know that young Barker is an enormous improvement on his predecessor as MP for Bexhill and Battle, Charles Wardle, who left Parliament to become a director of Mohamed Fayed's Knightsbridge emporium - where he lasted all of eight months.)
But why should Mr Barker be feeling virtuous? The virtuous act - assuming you share my MP's view that he can save the planet - would have been to send his Porsche Boxster to the car crushers, not to sell it. Mr Barker, having advised the odd Russian oil company in his time, is in no great need of funds. And, come to think of it, the sight of the Conservative environment spokesman directing a wrecking ball on to the brand of car most associated with conspicuous consumption would have been a political coup de theatre for the party which claims that "blue means green".
It's a tricky business, trying to be both ecologically virtuous and consistent. For example, we had Gordon Brown last weekend telling the world's leaders that they had to meet the moral challenge of climate change while simultaneously urging the Opec countries to step up oil production so that we all had enough of the black stuff. This newspaper - which leads the press campaign against man-made carbon emissions - had a front page headline on Saturday warning that the rise in the world's temperature "will put 400 million at risk" underneath a reader offer declaring "Win return flights to New York".
In the old days things were much simpler. The only thing that mattered for the car-buying politician -and I speak as the son of one - was that his constituents knew that his motor was made in Britain. My father, is of the generation that in any case would have thought it quite odd not to choose a British car. He had always driven Jaguars, and switched to Rovers when he went into politics, only because he felt that a Jag was a bit flashy for a representative of the people.
John Prescott has been mocked mercilessly for his two Jags. But if Ford, the owners of Jaguar, decide to close down the Coventry-based company - it has, after all, been losing about £400m a year - which leading politician other than John Prescott will be able to look the British workforce in the face? Certainly not David Cameron, who insists on being driven in a car made in Japan.