One of John Key's shortcomings when he entered politics was in the area of verbal precision. His off-the-cuff response to questioning sometimes betrayed a lack of due consideration. As Prime Minister, his performance has improved - but now the trait has come back to bite him.

Either that or he was badly advised on how he should respond to repeated questioning about allegations that Israeli spies were caught up in the Christchurch earthquake in February.

Whatever the reason, his initial reaction that any disclosure would not be in the "national interest" poured fuel on a fire that could have been extinguished almost instantly with the right emollient.

Prime Ministers are often loath to comment on speculation, especially if the topic involves national security. But Mr Key's choice of words suggested, most generously from Israel's perspective, that the Government suspected improper behaviour but had no proof.

Alternatively, they could be interpreted as hinting that the Israelis may, indeed, have been seeking to steal identities to clone a New Zealand passport. Either way, rather than maintaining good relations with Israel in the "national interest", as may have been his intention, Mr Key encouraged not only speculation but the idea that something might be read into the allegations.

The dousing eventually occurred several hours later as the Prime Minister, in the midst of a tour of the United States, acknowledged the public had a right to candid information. Yet this should never have been in question, especially as New Zealand authorities had found nothing amiss.

Mr Key revealed that the rapid departure from New Zealand of three young Israelis after a colleague was killed in the earthquake had triggered investigations by the police and the Security Intelligence Service. The agencies had also noted the pressure placed on authorities to let an unauthorised Israeli search and rescue team into Christchurch's red zone.

But the probes found no link between the Israeli backpackers and their country's intelligence agency, Mossad. "We don't expect Israel to [spy on us], but we have no evidence to support that they have," said Mr Key. "We simply have a very unusual set of circumstances."

The Prime Minister's slip-up was made more extraordinary by the fact that he usually has a good instinct for matters of public interest.

And in this instance, there was good reason for people to sit up. Still fresh in the memory is the attempt eight years ago by two Israeli agents to obtain a New Zealand passport. This attracted a strong public response from the then Prime Minister, Helen Clark. She imposed a set of sanctions that showed New Zealand was ready to defend the integrity of its passports, even when a supposedly friendly nation was involved. Only recently were diplomatic relations fully restored.

Mr Key's belated furnishing of information makes it clear there was nothing concrete to link the latest allegations with Mossad activity in 2004. But, notably, he was careful with his language, indicating he could not categorically rule out the possibility of illegal behaviour. Apart from the rapid departure of the Israelis, there seemed "a couple of other factors that just seemed odd", he said, while declining to go into detail. If this leaves a degree of doubt about the episode, it is possibly unavoidable, not least because Mossad has a reputation for stealthy dealings.

Because of this, it is hardly surprising that the suspicions of New Zealand intelligence agencies were aroused in the aftermath of the earthquake. The only real surprise was the ineptitude of a Prime Minister who chose not to put the episode in the appropriate context when first asked.