The Labour Party is 100 per cent correct in questioning the adequacy of the Speaker-instigated "investigation" into the use of the parliamentary travel entitlement by National MP Pansy Wong and, more pertinently, her husband, Sammy Wong.

It is not the fault of former public servant and now independent consultant Hugh McPhail that his report is unsatisfactory. He has largely had to take the Wongs at their word that the 13 overseas trips they took either together or separately on the perk were - apart from on one occasion - not used to further their extensive business interests.

Given that the allegations involved a (now former) Cabinet minister, such an inquiry should have been placed in the hands of Auditor-General Lyn Provost - not least because she is the watchdog on the spending of public money.

She also handled the inquiry into Phil Heatley's credit card purchase of two bottles of wine. The Wong case is more serious than that was.

Arguably, the matter should have been referred to the police, the case mounted against former Labour MP David Butcher providing the precedent.

As it is, McPhail found evidence that a trip in China from Beijing to Lianyungang did involve activity by the Wongs that could be construed as "private business purposes".

But we knew that already. That was the trip which found the Wongs out and prompted Pansy Wong's immediate sacking from the Cabinet.

It takes considerable faith in human nature to believe that was the only occasion on which business was conducted by the Wongs on the New Zealand taxpayer, who have subsidised their travel perk to the tune of nearly $55,000 over the past decade.

Without a further wider-ranging investigation, however, the public - like McPhail - has little option but to take the Wongs at their word.

The question now is whether Labour pursues the matter further. Having secured her scalp as a Cabinet minister, there seems to be little point in trying to repeat the exercise with an ordinary backbencher.

John Key is the winner. A byelection has been avoided in Wong's Botany seat. A slot in the Cabinet has been freed up to be filled by one of a number of senior National MPs fighting for promotion.

As usual, taxpayers are left feeling shortchanged. They get the grand total of $474.12 by way of the refund McPhail ordered the Wongs to pay for doing business on that one trip. A sum, of course, swallowed up by the fee paid to McPhail for his services.