Key Points:

The wait has been longer than Labour could ever have imagined, but the party was crowing yesterday with the full force of a barn full of chickens force-fed with vitamin supplements.

John Key had finally slipped up. National's leader had told the Herald on Tuesday he would have signed up to a New Zealand First-initiated compromise on the stalled Therapeutic Products and Medicines Bill had he seen it - and was still willing to sign up - only to change his mind yesterday after his remarks appeared in print.

Mr Key argues his initial statement was "misrepresented". Labour argues Mr Key's about-turn reveals that either he failed to grasp the detail of the compromise or was over-ruled by his colleagues when they saw his remarks in the Herald. What is less in question is that Mr Key has ended up very much on the defensive when it should be Labour that is embarrassed by failing to secure the numbers to pass the seemingly hexed legislation setting up a transtasman therapeutics agency.

Trying to get to the truth of why Labour and National failed to reach a compromise is a bit like choosing a herbal remedy off the shelf. There are many competing versions on offer.

At the heart of the row, however, is whether National was offered the opportunity to view the compromise proposal put forward by Winston Peters. National says it never saw it. National considers Labour's idea of "consultation" was unsatisfactory and unacceptable - and blames State Services Minister Annette King.

That may be the case. However, the Prime Minister stepped in at the last minute to try to break the impasse, and, according to Labour sources, sent a message to National through informal channels offering a full briefing on the proposed compromise.

Mr Key says he never heard about the offer. Either it did not reach him - he was overseas at the time - or it did and, according to Labour, he was over-ruled by health spokesman Tony Ryall and other colleagues who were opposed to the bill or did not see why they should bail out Labour.

None of this would matter terribly much had National happily taken the rap for blocking the bill, which, as the major Opposition party, it had every right to do.

However, National tried to have it both ways, arguing on the one hand that Labour's failure to pass the legislation illustrated the Government's lame-duck status, while on the other arguing it might well have supported the bill had Labour consulted properly.

National got itself into a muddle which - much to Labour's delight and thanks to Mr Key - has resurfaced in the week leading up to National's annual conference.

The fuss is unlikely to take the shine off what will be a triumphant first conference for Mr Key as leader. It is also too minor to end what the Prime Minister describes as Mr Key's "honeymoon" with voters.

But his vacillation will be seized on by Labour as an indication of his inexperience and vindication of its claim that other senior National MPs are really calling the shots, not him.

Whatever the truth of that, Mr Key will be kicking himself for giving Labour the opportunity to kick him it has been so desperately waiting for.