One of them is lying.

Unless either Act leader John Banks or internet tycoon Kim Dotcom turn out to be suffering from some delusional disorder or brain impairment – not likely, but something that cannot be completely ruled out – then one of them is telling outright porkies.

It is a measure of just how far Mr Banks has lost control of the row over the Kim Dotcom donation allegations that the Act Party leader is on the back foot.

After all, this is about allegations from a somewhat dodgy internet entrepreneur, who is not only facing international breach of intellectual property laws but – more pertinently – already has convictions for dishonesty.

Mr Dotcom is hardly Mr Credible.

But Mr Banks' initial response to the allegations was so full of fudge and bluster he is now the one looking shifty.

Yesterday in the House the Labour Party turned up the heat on Mr Banks.

Usually, in these situations, a fellow MP from the same side seeks a supplementary question aimed at providing a beleaguered MP with a launching pad for a counter-attack.

Even though Mr Banks does not have any fellow Act MPs, it is not at all unusual for an MP from an aligned party – say, one of the many National MPs who were in the House at the time – to feed such a question.

Yesterday: nada. Zip. National MPs studiously buried their heads in their order papers.

Yet National is probably the party which stands to lose the most from this row.

The Act Party is, to be blunt, almost dead on its feet.

But Labour MPs were as happy as pigs in muck yesterday, and it was not just because they were buoyed by that morning’s Herald Digipoll which showed a more than 6% jump.

Nor was it just that the party finally had an issue on which they could shove the government onto the defensive – an issue which does not involve Labour having to make any awkward decisions about its own policies.

Labour has a long-standing policy of moving to full taxpayer funding for political parties and effectively minimising any private donations at all.

It has never quite had the nerve to implement that policy, but it has been there for over a decade.

During the 2002 review of MMP the party, as a collective, and also in the form of several individual branches, made submissions to the review calling for full taxpayer funding of political parties.

Labour’s enthusiasm for the idea has grown as union membership – formerly the party’s main source of funding – has dwindled.

In 2008, then-Prime Minister Helen Clark told the House in an exchange at question time that “nothing would give me greater pleasure” than moving to a system of total taxpayer funding.

The idea is not particularly popular with voters – which is why Ms Clark, despite her clear enthusiasm for the idea, never quite had the nerve to follow through with implementation.

But it is there as a long-term goal.

The John Banks/Kim Dotcom row plays right into Labour’s hands on this.

The more discredited private donations to political parties looks, the better the chance of persuading a reluctant public to go along with full taxpayer-funded political parties.

Which is why – apart from the more obvious reasons of short term political advantage – Labour is talking up this issue for all it is worth.

As for the immediate issue, John Key has made it clear he takes Mr Banks at his word and the main thing which would cause him, as prime minister, to lose confidence in Mr Banks would be if the Epsom MP had misled him.

That sets the bar for dismissing Mr Banks fairly high.

The Act Party leader would have been not only dishonest but foolish if he has misled the prime minister.