Zac, are you serious? Of course I had read the Quality of Life group's report before I commented. In my piece I quote directly from it, and the main findings had been extensively leaked by your team for weeks beforehand.

I don’t want to become your sworn enemy. We both have scarier opponents to face, so I won’t deny that the discursive parts of the report are an excellent read. But it’s in drafting actual policies that the crunch comes, and upon careful reading of the policies you propose, the report did fall well short of expectations. It was, in other words, disappointing.

I said your proposals ‘fail to fully hypothecate’ eco-taxes into measures to help people be green. It’s true. Your reply that ‘some of the money’ from new green taxes would go to support rail clearly implies that the rest will be used for something else.

These are more than likely to be the top-rate income tax reductions proposed by John Redwood, which would provide nothing at all for people on average or low incomes – those who will certainly be hit hardest with new green consumption taxes. There is a big financial hole in the Tory’s tax plans and, as Shadow Chancellor George Osborne said in April, “any reductions in specific taxes will have to be balanced with tax increases elsewhere, most notably green taxes.”

We Greens recognise that the only equitable way to spend eco-taxes is to give them all back in subsidies that help people lead greener lives and therefore avoid paying the taxes in the first place: free insulation to cut your fuel tax bills, cheaper public transport to cut the need to pay petrol duty. Of course, this will inevitably shrink the money raised from eco-taxes – and that's the point.

Relying on eco-taxes to replace income tax betrays Conservative assumptions that poor people will not be able to change their behaviour and will therefore be saddled with eco-taxes indefinitely, while the rich celebrate their tax cuts with another holiday.

I seem to have caused the most offence by accusing you of offering new subsidies to nuclear power and of backing down on airport expansion, so lets look at these again in more detail.

On nuclear, as I said, the proposals do propose a new taxpayer subsidy for nuclear power at the expense of the onshore wind industry. The nuclear industry, which currently has to pay the Climate Change Levy, would not have to pay the proposed Carbon Levy. The report itself says so: “Nuclear would receive comparative competitive benefit from the EUETS [European Emissions Trading Scheme] and the carbon levy to recognise its contribution to carbon reduction.” (page 296)

Cancelling support for onshore wind is even worse. Under your proposals, onshore wind farms would have to rely solely on the Carbon Levy, meaning a drastic reduction in support for the only well-developed renewable technology we have.

You cite some NGOs welcoming the report, but two organisations that support an effective renewables policy have already voiced their concern about this move. The British Wind Energy Association said, “the proposals on wind energy would be a devastating blow to meeting Britain’s renewable targets.”

And the World Future Council, long-time supporters of feed-in tariffs for renewables, have even said your group is “misusing the term to provide a cover for its proposals that will dismember the UK’s renewables programme.”

Your temporary ‘moratorium’ on airport expansion is a long way from ‘explicitly ruling it out’. The most your report is prepared to accept is a brief pause for thought, before the aviation lobby eventually gets its way. Far from stopping new runways, this paragraph lays out the conditions for a 'go-ahead':

“There should therefore be a hold on all plans for further airport expansion in the UK while in each case such plans are tested against the challenge of climate change and in the context of a wider European agreement on the restriction of airport expansion. In this way the effect of expansion of our carbon footprint would be factored into the equation before any go-ahead on any of these projects is given.” (p 356)

And how about this on how the existing flights would be used? “This means reducing the rapid growth in short-haul flights with a shift towards the less price-sensitive business and long-haul leisure flights.”(p 355)

And “a fifth of the slots at Heathrow would potentially become available for longer haul flights – where no alternative exists.” (p 355)

This is fairly clear cut stuff. No reduction in flight numbers, with those that take off going further away. More carbon emissions from the UK’s airports, not less. And, apart from at Gatwick and Stansted, the way left open for airport owners to argue for more runways.

Finally, you tell me that Green voters “expect you to raise the debate, to celebrate and encourage best practice wherever it appears”. Well yes but, as Green politicians, our job is to fight for policies that actually work. Tricks like saying the right things while caving in on the details is exactly what I’m here to expose.

And if you want me to applaud your personal strategy of trying to promote green policies via membership of the Conservative Party, then of course I won’t. I’ve chosen a different way for a very good, practical reason. You will get more real action from the other parties by challenging them at the ballot box and taking their political power, than you will by joining their fast-track internal promotion schemes.

Even though we are small and not elected everywhere, the pressure we exert when we do well at the ballot box can be immense. The largest green policy shift in this country’s history famously took place shortly after the Greens gained 15% of the national vote in the 1989 Euro elections. We threatened their power, so they changed their ways. No vocal minority of green-minded Tory back-benchers could have achieved that.

Our two London Assembly members have more influence on London’s policy framework than any Tory in the GLA because we hold the casting vote every year on the Mayor’s budget. Without our support it doesn’t pass, so we have steadily increased the amount of hard cash going into the fight against climate change in London (£150 million this year) while the other parties have to sit on the sidelines. Norwich City council now plans to reduce carbon emissions by 6% a year, thanks to 12 Green Councillors, and just three Greens in Kirklees helped turned Huddersfield into the solar power capital of the UK.

I think in the end you will learn the mistake you have made. At the next general election, both you in Richmond Park and Green MEP Caroline Lucas in Brighton Pavilion are likely to be elected to Westminster.

Caroline will be free to say what she likes, heading up the new Green Party opposition group. You, on the other hand, will have to negotiate with people who have very different feelings about what is acceptable to say to their voters. You will also have to steer a tricky course between your advancement in the party and saying what you really believe. I think you will have some painful decisions to make, and you may find that Caroline is saying the things you can only think.

Read Zac Goldsmith's article responding to Sian's original post