Tim rightly attacks the economic illiteracy of Squit the Younger; why the heck does he want to "find ways to increase...the quantity of money"? He's also right to point out that market mechanisms are the way to protect the environment.
I suspect, though, that it would be unwise for the Stupid Party to explore this idea, good as it is.
If market forces are to protect the environment, clear property rights must exist. In the classic problem of the tragedy of the commons, common land gets over-grazed and destroyed precisely because no-one owns it, and so no-one has an incentive to protect it. If someone owned the commons, they could charge people for using it, thus protecting the land.
Free-market environmentalism, then, requires the assignment and definition of property rights: to preotect the environment, someone must own it.
But to whom do we give ownership? The Coase theorem says it doesn't matter, from the point of view of efficiency. As long as there are no transactions costs and free capital markets, the same economic activity will occur. So, for example, if environmentalists owned the Arctic National Wildlife Refuge, oil companies could pay them for the right to extract oil. Or if oil companies owned it, environmentalists could pay them not to drill.
Sadly, though, this is too simple. Even when the Coase theorem is right, the allocation of proerty rights affects the distribution of wealth. And the assumptions underpinning the Coase theorem rarely apply. In particular, there's the problem of the endowment effect; once people own something, they value it more highly than if they don't. That means ownership matters for efficiency, as well as equality.
So, when we ask: how can we use markets to protect the environment?, we must ask: how should property rights be assigned?
And herein lies the danger for the Stupid Party. If we start asking about how we can use property rights to protect the environment, we might start asking some really embarrassing questions, like: are there other ways in which a (re-)assignment of property rights might be good for us? How do property rights emerge anyway? Is the current distribution of them consistent with philosophic accounts of what legitimate ownership means?
This opens a really nasty can of worms for the Stupid party. If I were them, I'd heed the advice of William Blackstone, to keep quiet about the subject:
There are very few that will give themselves the trouble to consider the origin and foundation of this right [to property.] Pleased as we are with the possession, we seem afraid to look back to the means by which it was acquired, as if fearful of some defect in our title; or at best we are satisfied with the decision of the laws in our favour, without examining the reason or authority upon which these laws have been built.
More stuff: Here's Garret Hardin's original essay, The tragedy of the commons. And here's a great analysis (pdf) of the issues involved in assigning property rights over the environment.
Another thing: Tim says: "Zac Goldsmith...wouldn’t know a decent economic argument if you slapped him in the face with it." I'd like to see this hypothesis tested, frequently.