ALL three main political parties want to colour themselves green, but yesterday's Budget shows how difficult that will be.

Gordon Brown made much of, belatedly, giving pensioners free national bus travel. If he had been really green, it would have been free national rail travel - but that, at a time when our mainlines are almost unpleasantly overcrowded, would have been too expensive.

And if he had been really serious about green travel, he would have increased the duty on air fares and made us pay the real cost of flying. He didn't, and so airlines will continue to entice us to take wholly unnecessary journeys to the other side of the world for less than the price of a packet of crisps.

But if Mr Brown had put up air tax, he would have been committing political suicide. Every family nowadays expects a cheap week in the foreign sun - no politician would dare deny them.

Are the political costs of saving the planet too high to make the planet worth saving?

Another line in Mr Brown's Budget stood out.

He said: "With 98 per cent of emissions occurring outside Britain, climate change is a global issue which demands global solutions."

Whatever we do in this country is welcome and we should be doing far more than we are. It is to David Cameron's credit that he has pushed the environment so far up the agenda that Mr Brown has taken notice.

But whatever we do in this country, no matter how many 4x4s we drive off urban roads, it will be just a speck of carbon in a polluted atmosphere.

For all the 25,000 turbines and panels that are about to sprout on British public buildings, probably a greater contribution that this country can make to the environment is to use our special relationship with America and force the President to mend his country's polluting ways and to roll out clean technology to developing countries.

No-one in the world is better placed to do this than Tony Blair. What a legacy that would be for him to leave behind.