It is hardly surprising that National Party leader Don Brash says he would be "uneasy" about foreign affairs officials sitting in on his future meetings with overseas delegations. He can hardly have expected that a comment he is alleged to have made to visiting United States Republican senators would find its way into the public domain. Nor, under any circumstances, should it have. The Prime Minister's decision to air the comment was an appalling departure from convention.

What Dr Brash supposedly said - that if it were up to him, the ban on visits here by nuclear-propelled ships would be "gone by lunchtime" - is not the issue, whatever Helen Clark claims. Her breach of trust is. The convention for such meetings is that Foreign Affairs staff attend, keep a record and circulate it on what the State Services Commission terms a "classified" basis. There is nothing to suggest that Foreign Affairs staff acted inappropriately on this occasion; that they alerted the Government about the political significance of Dr Brash's comments. What was inappropriate, and utterly unethical, was the Prime Minister's crass use of their record for political purpose.

It is, of course, easy to see why the Prime Minister might have been tempted to breach convention. The National Party's effort to navigate a way out of the nuclear-ships impasse with the US has produced the most feeble of attempted compromises. Its unwillingness to take a strong position, out of fear of alienating a recently reinvigorated support base, leaves it open to criticism. But to try to exploit this by publicising a private meeting is way beyond the pale.

A spokesman for the Minister of Foreign Affairs has as good as admitted this. While prevaricating over whether Phil Goff would release the record of what Dr Brash said, he noted that anything said by the six senators during the January meeting would remain confidential. It could not, under any circumstances, be released publicly. In other words, as far as the Americans were concerned, the talks were private. This unequivocal view of the convention was reinforced by the US Embassy. "As a matter of practice, the embassy does not discuss private exchanges between official visitors and their counterparts," it said.

Such conventions survive only if they are not abused. The Prime Minister has effectively undermined this one. Quite logically, Dr Brash will be inclined to steer clear of involving Foreign Affairs officials in future meetings, whether at home or abroad. Already, there are suggestions this will be the case for his upcoming trip to the US. If such is so, Dr Brash can at least be sure there will be no record of his discussions available for misuse by the Government.

Regrettably, however, such a reaction has a considerable downside. First, it creates an information vacuum. It is important that Foreign Affairs officials know what political parties outside the government are discussing with overseas politicians. If there are to be seamless transfers of power, they must be aware of, and prepared for, different policy approaches. A leader of the Opposition also has an ease of access to overseas political leaders that is usually denied ambassadors and other embassy officials. That, as the Prime Minister has acknowledged, is a "tremendous advantage" to the Ministry of Foreign Affairs and Trade, and to New Zealand.

Foreign Affairs officials are said to be upset by the Government's use of the report of Dr Brash's meeting. So they should be. They have every right to expect that reports written on a classified basis will not be used for cheap political gain. In one swoop, Helen Clark has soiled an important tool of their trade. No matter how great the temptation for a Government on the backfoot, it had to be resisted. A Prime Minister should never put a party's interests ahead of principle.