The Green party has been likened to a watermelon: green on the outside and red on the inside. But that is to do a huge injustice to generations of socialists and communists. Misguided though they were in many of their ideas, nobody could accuse them of actively seeking to make society poorer.

That, however, is the unashamed aspiration of Natalie Bennett and what has become the fastest-growing political party in Britain. It is quite possible that a good proportion of the 9 per cent of the electorate who say they are planning to vote Green in May are unaware of this, but it is there in black and white (‘policy EC201’) on the party’s website. It states that the party wants to pay every-one a ‘Citizen’s Income’ — which has since been put at £72 a week — in order to allow ‘current dependence on economic growth to cease, and allow zero or negative growth to be feasible without individual hardship should this be necessary on the grounds of sustainability’.

The three main parties have been happy to cast accusations of extremism at Ukip, yet they have missed the real extremist party in their midst. There is nothing to be welcomed in a shrinking economy, not even with £72 a week to compensate you for your lost job. If a depression were a reasonable price to pay for an improved environment, Tyneside in the 1930s would be remembered as a paradise. No doubt the air became cleaner as shipyards closed, yet those who lived through the Great Depression tended to remember it for other reasons: hunger and desperation.

Of course, everyone should be concerned about the environment, but to think that it is best-served by self-imposed poverty is folly. Pollution from industrial activity has fallen hugely since the 1930s, not because we have held back from wealth creation but for the opposite reason: we have learned how to do things better. We have learned to mitigate the problems associated with rich societies rather than retracting into a form of pre-industrial existence.

The Greens have produced reams of grand ideological policy, in which people subsist in localised economies and practise barter without the need for horrible bankers, yet when they are faced with a genuine environmental challenge they have been found wanting. Brighton, the one council they run, languishes at 306th out of 326 English councils for its recycling rate. Only a quarter of its rubbish was recycled in the last year, compared with two-thirds for the best authorities. For a supposedly green party, this is an astonishing failure.

When off the subject of the environment, however, the policies get even sillier. Only the Green party could propose to shrink our armed forces, end the arms industry and simultaneously make it legal to be a member of Isis or al-Qaeda. No one but the Greens could want to decriminalise hard drugs and yet outlaw pâté.

Ukip is rightfully often damned as a party of Little Englanders, but they are not nearly so little as the Greens. Ukip is at least consistent in wanting to leave the EU so that Britain can better face the world and adopt its own immigration policy. Natalie Bennett appears to believe (she said so last Sunday) that Britain could remain a member of the EU while imposing import taxes on all foreign goods. Such taxes would leave Britain open to billions of pounds in EU fines, yet in the Greens’ bizarre little world no conflict seems to arise.

It is a proud aim of the party to reduce international trade, something which absurdly they seem to think can be done without harm to developing countries. Whether they like it or not, however, this would boost one sort of British export: money and assets, which would be siphoned out of the country at great speed if the Greens’ proposed wealth tax ever looked like happening. It is a symptom of the Greens’ lack of grip on reality that they think they could raise £45 billion in a wealth tax on assets over £3 million. France, which has a wealth tax starting at £800,000, manages to raise less than £4 billion. As they have found, imposing a wealth tax means that wealth starts flooding away.

The rise of the Greens has only become possible because of the growing mood of resentment against the established parties. It is true that the Conservatives and Labour have behaved as a duopoly for too long, have taken their voters for granted and deserve a challenge from elsewhere. But the emergence of other parties — and indeed the record of the Liberal Democrats in the coalition — has shown that for all the bickering, false promises and occasional contempt for the public shown by the established parties, they nevertheless have a professionalism which is absent from the upstarts.

In most elections, of course, the Greens would not matter. They would act as a receptacle for protest votes without anyone having to take their policies seriously. But the dynamics of this year’s vote are very different. It is looking increasingly likely that the only way to establish a majority in the next parliament may be for three parties to establish a coalition. The Greens could well be one of them, allowing a few of their policies to reach the government’s legislative programme.

It is improbable that any other party will adopt the Greens’ plans to throw the country into recession, but it is difficult to see how any of its policies could sensibly make it into a coalition agreement. The term ‘unelectable’ is overused, but in the case of the Greens and their pernicious ideology, it is appropriate. Even as the most junior member of a coalition, this party is not fit for government.