Steve Richards: In the crucial battle for the green vote, Labour is losing out to the other parties

The anti-Tory alliance that gave Labour power is fracturing, and the environment is part of the reason

Stand back and consider two tiny mini-elections that took place in recent days. Last week Labour lost a local by-election held in Kentish Town in north London. It did not lose by a tiny margin. The party was slaughtered. The Liberal Democrats won. The Greens came second. Labour was third.

This week there was an even smaller election. A friend asked her students at City University which party they planned to support at the next election. The Conservatives won on the basis that the voters considered David Cameron to be the greenest of the party leaders.

Here are two disparate tiny samples, but taken with more substantial evidence they suggest that climate change is not only having a dramatic impact on the planet, but on the shape of British politics as well. The by-election points to a real danger for Labour on a national basis.

Probably the Greens will not win any seats at the next general election, but it is possible that along with the Liberal Democrats they will split the anti-Conservative vote three ways. The informal anti-Tory alliance that propelled Labour to power for three general elections is fracturing and concerns about the environment are part of the reason why. The Lib Dems' national rating remains robustly solid and the Greens are making some headway in parts of the country.

Over the past year the Conservatives have performed erratically in by-elections and opinion polls. In some places, such as Kentish Town, their support was virtually non existent. But their one relatively strong performance was in the May local elections when Cameron conveyed a single message: vote blue and go green. Cameron reflects privately that a lot of friends and advisers thought he was daft to focus so relentlessly on the environment in those elections. It worked. My friend's students might not be alone.

At the very least Labour should be asking itself as a matter of urgency how it has got into a position where the environment is beginning to become an electoral threat rather than an opportunity. This is a much harder question to answer than it is to pose. Gordon Brown is criticised widely for failing to impose more green taxes, in particular for not re-introducing the fuel escalator in which petrol prices rise higher than the rate of inflation.

But much of Britain is at a phase where it is intensely green until it is presented with a massive petrol bill. For many public transport is currently too expensive and useless to offer a viable alternative, although the Transport Secretary, Douglas Alexander, made a significant announcement earlier this week. He plans to give local authorities new powers to raise the standards of the private bus companies, many of which run hopelessly inadequate monopolies. In some parts of the country the prospect of improved buses could be a "green" lifeline.

In the wider context beyond buses the Environment Secretary, David Miliband, makes tonight one of the most important speeches delivered by a cabinet minister since the last election. Miliband will offer a political route map for Labour in relation to the environment with a daring clarity and sense of context that is rare in the debate, especially since the frenzied posturing across the political spectrum following the publication of the Stern report.

Miliband is able to be politically bold partly because of his own unusual position. He is the only cabinet minister who has been pressed by colleagues and parts of the media to stand for the leadership and consistently declined to do so. In a strange way this makes him more powerful than some of those that aspire to ultimate power.

If the Home Secretary, John Reid, makes a speech it is seen party through the prism of his unresolved personal ambition. When half the cabinet make speeches they are doing so with the deputy leadership in mind. For now when Miliband delivers a speech it is easier to brush aside the clamour of noisy ambition and hear what is being said.

In tonight's speech, Miliband intends to analyse why the other political forces are less well equipped to tackle climate change. He will dismiss the "deep green" option of a zero growth strategy as an excuse to cement the existing disparities in wealth and power across the globe. He will point out also that the "blue- green" strategy is doomed to failure because of the Conservatives' hostility to the state and reliance on market-based solutions.

He will point out that climate change is the biggest example of market failure as prices do not reflect the cost to the environment. With a nod towards the Conservatives' persistent Euro-scepticism he will argue also that climate change challenges their idea of national sovereignty over decision-making. Climate change is the defining example of interdependence.

This will give him space for what he regards as the "red green" options. Given Brown's caution on the issue Miliband will be mischievous enough to suggest that Labour should adopt a new golden rule to accompany the famous rules laid out by the chancellor. The rule would aim to establish a low carbon economy.

He will call also for a New Deal that will provide help, training and financial rewards in relation to specific green initiatives. Note the nods to the mid-1990s with his new deals and golden rules. I am told that in his speech tonight there will be many more references to other policies that brought Labour to life then, but now Miliband roots them all in the need to tackle climate change. In essence, he will argue that the environment needs Labour, but Labour needs the environment, pointing to an entire agenda in which the party can renew itself through a commitment to this policy area.

Miliband's speech will raise many unanswered questions. He cites important targets without highlighting in detail some of the painful measures that might be required to meet them. There is no certainty that his vision will be shared across the Government, not least by the cautious Chancellor, let alone the European Union and other parts of the world. Possibly, he underestimates Cameron's willingness to use some instruments of the state in dealing with green issues. At times the speech is artfully political, establishing dividing lines that are a little more blurred.

But for all the inevitable qualifications Miliband offers a way forward for a government that is perversely in danger of losing support on an issue when it should be strong. He does so by linking his party's values to a precise policy area, a model that his colleagues would do well to follow. Some ministers might read the speech and conclude that it is all too damned difficult. They would be wiser to regard it as an opportunity and remember the voters in Kentish Town and those youthful students who contemplate voting blue to go green.

s.richards@independent.co.uk