His 10 years as Chancellor have offered little evidence of concern for green issues, but his desire to be viewed as a more rounded individual before his move to Number 10, has seen him develop a sudden new interest in the subject.

Brown made a promising start by commissioning the report from Sir Nicholas Stern which, in clinical language, laid out the dangers of failing to address climate change – a considered document which is now being read by governments around the world.

However, his subsequent record has tailed off dramatically. The Chancellor's latest intervention was a move in this week's Budget – trailed heavily in advance – to double road tax on 4x4 and sports cars, just a few months after he raised the duty paid by every passenger who takes a flight.

Even though there is little evidence that either of these actions will have a significant effect on carbon emissions, they will certainly succeed in making it harder for a Brown government – or any future administration for that matter – to use the tax system as part of a coherent climate-change strategy.

The rise in air passenger duty was not set at a level high enough to stop people flying, but it was sufficient to annoy those who were suddenly presented with an extra unforeseen cost as they prepared to travel.

Buyers of cars costing tens of thousands of pounds are unlikely to choose something more economical on the basis of an annual £400 charge, but they will wonder what they are paying for when they have to fork out more at the post office.

Critically, Brown has also failed to ring-fence this extra tax revenue for improvements to public transport or other measures which might actually help the environment and fund schemes such as the Leeds Supertram. Instead, the cash disappears into the black hole that is the Treasury.

So, the first experience thousands of people will have of "green taxation" is of a blunt tool which hits them in the wallet and leaves the amount of C02 being pumped into the air virtually unchanged.

While significant questions remain over whether the Tories' climate-change policies could ever be put into practice, or have the desired results, they are at least underpinned by two fundamental principles that will be critical in winning public support for similar ideas in future.

First, the Conservatives have promised taxing pollution will replace other taxes and not just add to existing ones. Second, they have focused on tackling excesses – those who fly the most often – rather than hitting everyone with the same-sized stick.

Brown's approach couldn't be more different. Car tax does not vary depending on how often, or how far, a motorist drives, or whether they could have used public transport.

Air passenger duty is a flat-rate charge regardless of whether it is the first flight that a passenger undertakes in any one year, or their 10th trip. Furthermore, the Chancellor has not offset these tax rises with reductions elsewhere.

At present, the British public is split broadly three ways on the climate-change issue. One group considers the science proven and is already trying to do what it can to be greener. A second section of society remains open to the idea, while a third is deeply sceptical.

Brown's taxes will do nothing to help the first group. They will disillusion the undecided and they will harden the opposition of those who regard green taxes as yet another money-making exercise for the Treasury.

Regardless of how they use them, politicians of all sides should be cautious before choosing taxes as their principal weapon against climate change, especially as the market is already producing results.

Changing public perceptions has led to falling sales of 4x4 vehicles, while, following pressure from customers who want to make ethical choices, Marks & Spencer has started labelling food flown into the country. These are small changes but they reflect significant changes in attitudes in Middle England.

The current debate is also overly dominated by talk of punitive measures rather than offering encouragement for people to be green.

Brown's final Budget announced higher landfill taxes, but no measures to encourage recycling still further. There was also no significant new funding for major public transport projects. And, while he extended tax breaks on biofuels to 2010, the Chancellor admitted that they will still only represent 10 per cent of the market by then.

But, if the scientists are right, a future Government may have no alternative other than to raise taxes to bring about dramatic changes in behaviour.

That option should certainly be kept open. However, if Brown's blunt approach continues, public support for green taxation will have evaporated by then.

Fictional Prime Minister Jim Hacker was once advised by Sir Humphrey that "masterly inactivity" was always a prudent course of action.

Climate change is too important an issue to be used simply as fodder for Gordon Brown's image-makers. Until the Chancellor has coherent policies to offer on climate change, he would do well to take Sir Humphrey's advice.