OPINION: The Government is starting to look rattled over opposition to the Trans-Pacific Partnership Agreement. Perhaps its internal polling is showing a genuine groundswell of concern. Or perhaps it is just telling it to meet fire with fire.

Either way, National's response looks arrogant. Prime Minister John Key's reaction to a large protest march in Auckland, and a smaller one in Wellington, was dismissive and unpleasant. He said a third of the demonstrators were rent-a-crowd protesters who opposed any free trade deal, and another third were Labour and Green supporters who opposed anything the Government did. Presumably the last third were acceptable opponents.

These personal remarks sound like the high-handed remarks of a Government in power too long. They look badly out of touch. Free trade deals are no longer automatically accepted by a majority of voters. Key should recognise this and start trying to meet the concerns rather than insulting critics.

And it won't do to resort to bromides. It doesn't automatically follow that "free trade" deals with big markets will be a net gain for New Zealand. First, these deals are almost never "free trade" deals. They are at best agreements to widen access to markets. And it is clear that access to United States and Japanese dairy markets, which could be a serious economic gain for New Zealand, may never happen.

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Trade Negotiations Minister Tim Groser has said as much. Presumably this was not simply a negotiating position. Groser has shown a similar arrogance to Key's, especially his remark about leaving it to "the grownups" to get on with the negotiating. Apparently the adults are having trouble managing to do this.

Key dismisses all objection to the secrecy of the talks, and asks when any previous deal has been made public before it was signed. This puts things around the wrong way. Concern about the deal, and what it might cost New Zealand, means that voters are much more bothered by the secrecy than they ever were before.

And this concern is shared not just by know-nothing lefties and extremist ideologues, but respectable economists of various sorts. Deciding whether the deal is a net benefit or liability is a complex calculation. These complexities do not disappear in a puff of prime ministerial smoke.

Key might be right when he says Pharmac will not be harmed by the deal, but voters are sceptical and certainly won't take a politician's word for it. They will wait to see the fine print – if there is an agreement at all – and they will want to hear expert opinion.

Key's great gift as a politician has been his uncanny ability to sniff the wind and respond to it. Normally this involves a super-relaxed demeanour and a policy response that goes just far enough to persuade just enough voters to back him.

But right now Key is being contemptuous of his critics. That won't win this argument, and it might cause real damage to his standing