Are the Greens the only left-wing party left in Britain?

The Labour response to the Greens makes them sound like Tories. The Greens are soft on drugs, they say. They'll bring in higher taxes and pay out more in benefits.

It's a telling response, because it vindicates the central argument Caroline Lucas will make at the party convention in Birmingham tomorrow: that the Greens are the only left-wing option available to British voters.

She'll say:

"Labour has not only consistently failed to challenge the illiterate economics of George Osborne's slash and burn approach to public spending, but Ed Balls has signed up to the same spending limits as the government itself. Secret courts as part of the justice and security bill? Labour refused to oppose [them]. On the appallingly illiberal immigration bill, they abstained. They support workfare sanctions. Even on the issue of bringing the railways back into public ownership – a hugely popular policy – Labour has flunked it."

The Greens are doing well. They won 6.6% of the vote in May's local and European elections. Polls suggest they could win six per cent in the general election too, a significant increase on the 0.9% they won in 2010.

The party has popular policies on issues like nationalisation of the railways. Its leader is Natalie Bennett, an Australian former journalist, but it enjoys this informal triumvirate of female leaders, with Lucas leading in the Commons as the party's only MP and former mayoral candidate Jenny Jones in the Lords as its only peer.

They face a major fight with Labour for their single Brighton seat, but will target seats like the Holborn and St Pancras – where Bennett will stand – as well as Norwich and Bristol.

There are problems. The party struggles to win media attention. Partly this is because the media has an in-built bias against left-wing parties. But Green complaints along these lines can come across as conspiratorial. The truth is Bennett is not the most charismatic of leaders and interviews with her are often a bit too worthy. It lacks a figure of the Faragist mould, capable of commanding the camera's attention.

The party will also struggle to keep its vote up at a general election where Labour voters know that every seat is vital. To opt for the Greens potentially takes away Labour's role as the bigger party in a hung parliament. On the other hand, the Greens can appeal to voters to give them a chance to be king-makers in a hung parliament, as Ukip are. Which way the voters go will depend on how sick they are of the three main parties. They may be sicker than we realise.

And then there is Brighton. The party's record in the constituency is decidedly mixed. Council charges have soared while services get a critical write-up. A strike by refuse workers was opposed by the council leader while his deputy joined the picket line. There are also the traditional idiocies of a protest party in its first few years in power – things like meat-free Mondays in council-run canteens, which died an ignoble death, or the 'no fracking zone' policy, which applied to an area where there were no plans for fracking.

But these are inevitable growing pains for a party unused to power. And once you open up the hood and look at policy, the Greens have some decent, economically literate, solidly left-wing ideas.

Crucially, the party understands that a consumer economy can only operate with workers who are actually paid enough to buy things. Osborne's recovery is turning Britain into a part-time economy. Employment may be up, but the type of employment is dispiriting. The self-employed account for over 80% of the net rise in employment since 2008. Zero hours contracts abound. Earnings rise pitifully. A casualised workforce is scratching a living. No wonder so many British high streets are ghost towns, with boarded up shops lending many towns an air of despondency.

Today the Greens will unveil a policy for a rise in the minimum wage, currently set at £6.31, to the living wage, which is £7.65 and £8.80 in London. They want this up to £10 for all by 2020, the end of the next parliament, with the minimum wage then linked to living costs.

Business groups say such policies are unaffordable and will see businesses close down. They warned the same thing ahead of the introduction of minimum wage. In fact, the international evidence does not support the idea that a minimum wage results in a loss in jobs.

In 1992, economists David Card and Alan Krueger gathered information on fast food employment in New Jersey and Pennsylvania. The former had increased its minimum wage by 18.8% and most economists expected employment to fall, all other things being equal between the neighbouring states. In fact, employment in New Jersey restaurants grew slightly. The right has been unable to substantiate its insistence on an effect on employment since. Higher wages have a minimal or even non-existent impact on employment.

But low wages do have an impact: they force people to claim benefits, usually but not exclusively through tax credits and housing benefits. They keep people on benefits, because taking up work doesn't make financial sense. They push people towards private credit, which could still cripple our economy if interest rates rise. They stifle demand. Paying people decently, as the Green party seems to recognise, is not kindness. It is economic competence.

The party also supports the idea of a citizens' income. They've had it for a long time but recently confirmed they were putting it front and centre of their election campaign.

This policy would pay out to everyone – employed or unemployed – every month, at roughly the level of unemployment benefit. Virtually every other tax relief and allowance would be phased out, although housing benefit, which is something of a whopper, would remain. The policy would address the concern Tories often claim to have about the disincentives to people leaving benefits, because work would only increase their income. It would get rid of the complex tangle of rules and regulations around benefits better than Universal Credit ever will and chip away at the shadow economy. Its universality would remove the stigma of benefits. It may also encourage entrepreneurism, by giving people the confidence to start a business, safe in the knowledge they have a safety net if things go pear-shaped.

This type of daring policy seems so open to ridicule that most mainstream parties won't touch it. But it can be explained to the public. The case for it can be made by a party with the bravery to make it. The Greens plainly have that. Their positive message on immigration – alone in Westminster – civil liberties and rail nationalisation demonstrates that. They're to be commended for moving so radically out of the limitation of environmental policies.

With a hostile media and a tight election, there is a definite limit to what the party can achieve. But it is performing strongly in the polls and in its manifesto. It deserves more recognition than it gets.