Maori Party co-leaders Pita Sharples and Tariana Turia are proving to be politicians of principle who know which side their toast is buttered on.

The Maori Party co-leaders' opposition to the emissions trading scheme fell the moment National's negotiators promised some sweeteners.

They have secured free insulation packages for houses in areas where low-income Maori live.

But what does that particular promise tell you about New Zealand today if the National-Maori party initiative is not also made available to all other Kiwis at a similar income level, regardless of ethnicity or colour on a pro rata basis.

What really stinks is the fact that Sharples and Turia are now in secret negotiations with National over the extent to which Maori - as opposed to those of all New Zealanders - will be able to protect the future value of their assets from being eroded through major Government policy changes.

What is at stake here is not simply the argument that Maori leaders made last year during the run-up to the passage of Labour's emissions trading scheme legislation.

They claimed then that the ethos of the Treaty of Waitangi would be broken by the deleterious effect of the scheme on the valuations of their interests in the forestry, fishing and farming sectors.

Neither Environment Minister Nick Smith nor the Maori Party negotiators are saying anything in public on this score yet.

But if the Maori Party is able to secure a deal - which opens the door for previous Treaty settlements to be opened up again so Maori can be compensated for the effect of the impact of the emissions trading scheme on asset values for land, forestry and fishing - it won't stop there. The genie will be out of that particular bottle for once and for all.

Maori last year argued they could be owed as much as $2 billion in compensation if the land currently in forests could not be converted to potentially more profitable uses. But Labour would not buy into the argument.

It is hard to credit that just weeks back, the Maori Party issued a minority report taking issue with the outcome of the parliamentary select committee reviewing New Zealand's emissions trading regime.

In essence, the party continued to oppose the introduction of an emissions trading scheme and "would do so more strongly" if a replacement scheme was to be less effective and more inequitable than Labour's existing scheme.

The Maori Party was unconvinced the market was the best mechanism to set a carbon price: "The continued rise in oil costs from pending peak oil production and global shortages of fresh water alert us to the fact that the world's economy is not so much in a temporary recession as in a state of major change, and that the current mode of living in developed countries is simply not sustainable into the future."

The representative Sharples and Turia assigned to the committee - Maori Party MP Rahui Katene - went further: "The time is past for scheming and trading - we want an Emissions Reduction Programme. We want a regime that is transparent and fair, and requires polluters to pay."

The deal National unveiled on Monday is hardly in the "forcing polluters to pay" category.

In reality, Sharples and Turia had been given the message by their people that by sticking with their party's longtime "polluter pays" rhetoric, they were simply standing in the way of commercially-minded iwi and corporations to screw a good deal out of the National Government that would shift much of the liability for greenhouse emissions away from the sectors in which Maori are invested.

Maori are major players in the primary sector.

They have more than 25,000ha in dairy farms, they own forest estates (200,000ha of pre-1990 exotic forests and 400,000ha of pre-1990 indigenous forests as well as 200,000ha of scrub); they also own 35 per cent of the fishing industry.

The constitutional stakes are high.

The deal the National Party's top negotiators and the Maori Party co-leaders are now negotiating must be subject to select committee scrutiny.

But why stop there?

The newly minted National Government told the United Nations' Climate Change conference in Poznan last December it was undertaking a review of the Labour's Government's emissions trading legislation to "find a politically durable way of moving forward by building a wider policy consensus".

What National should be doing is reopening talks with Labour. Labour has now stated its bottom lines.

Among other areas it would likely agree to the Government's proposed date for the inclusion of stationary energy and transport into the scheme; it would have likely compromised on the entry date for agriculture.

Frankly, if the Government is serious about a durable solution it should get back to the table with Labour and stopping paying the Maori Party's piper - that tune is just too expensive for all of us.