Key Points:

Asked if he was going to Sir Robert Muldoon's funeral, a National Party Cabinet minister, who must remain nameless, confided at the time that he would be there if only to satisfy himself that the lid of the coffin had been nailed down properly. It was a statement made only partly in jest.

Between his relinquishing the leadership of the National Party in 1984 and his death in 1992, Sir Robert kept up a regular commentary from Parliament's backbenches on the failings of his successors.

Until yesterday, Helen Clark had been spared the headache of a former leader running amok. Of her more immediate predecessors, David Lange somehow managed to bite his tongue when he thought things were going awry, Sir Geoffrey Palmer has remained fiercely loyal to her, and Mike Moore, barring the occasional opinion piece, had seemingly closed the door on domestic politics.

Yesterday Moore chucked a rather large incendiary device through that door by claiming the Prime Minister's hounding of opponents echoed some of the worst features of Sir Robert's prime ministership.

Having made the explosive impact he had obviously intended, Mr Moore then suggested he was really "teasing" and being "humorous" in comparing Clark with Sir Robert.

No one believes that for a moment. The Prime Minister will be struggling to see the funny side of being tagged as "Muldoonist" - one of the more stringent insults you can hurl at someone in politics.

She will have seen nothing funny in the timing of Moore's attack even if she is officially laughing it off so as not to give it more legs.

In recent weeks, Labour has been so consumed with sorting out political sideshows of little long-term importance or scoring points off John Key that it has looked like it is already electioneering and no longer governing.

The last thing Labour needed in a week when it is refocussing on displaying the fruits of governing - the new Gold Card for superannuitants, for example - was another distraction.

However, judging how damaging Moore's outburst is to Labour requires separating the message from the messenger.

The message that Clark is Muldoonist will resonate positively with those who already cannot abide her. Those who favour her will view the attack as over the top.

Clark has not crossed the boundaries which define "Muldoonism". By example, she has never used information gathered by the Security Intelligence Service for blatant political ends as Sir Robert did in outing members of the Socialist Unity Party. No journalist has been banned from her press conferences because of what they have written.

As for the messenger, Labour realises Moore is getting attention only because of his credentials as a former leader. While keeping the Prime Minister out of it, Labour's tactics have switched from ignoring Moore to trying to discredit him by exposing his motives as self-interested.

He thus still holds a grudge at being ousted as leader by Clark. He cannot accept no longer being in the limelight. It's revenge for him not being invited to Labour's 90th birthday celebrations.

However, the suspicious in Labour's camp will fear Moore was out to destabilise Clark for political reasons not personal ones, conceivably as part of some longer-term campaign by those on the right to install Phil Goff in the leadership.

Moore now says he was issuing a general wake-up call to Labour. However, he may instead have rung alarm bells with those on the left.