Some people are fond of saying "we all know what happened" to cause Labour's Falkirk parliamentary selection row.

Thus far, what we actually know is that the party and Police Scotland have each failed to make anything at all of this sure and certain knowledge.

Allegations are plentiful. Some are serious. They go far beyond the traditional, unedifying business of organising on behalf of a favoured nominee. They amount - allegedly - to an attempt to manipulate a local party's membership list in an effort to fix the selection vote.

Dispassionately, that sort of claim shouldn't be too hard to prove, but Labour have provided their own complications. If, for example, the Unite union recruited "around 100" new party members and paid their dues it was acting, like it or not, under the rules as they existed. For comedy's sake, those rules were introduced when Tony Blair was party leader.

If the union signed up people without their knowledge and consent, however, that is another, more serious matter. If some then complained about being treated in this manner but were later persuaded to withdraw their complaints, the business becomes murkier still. Do we know this happened in Falkirk? We do not.

Patterns have been discerned, patterns that have been deemed suspicious by some. Credulity has been stretched in certain quarters. The failure to publish the report of a Labour inquiry is held to be significant. An industrial dispute at the Grangemouth plant is introduced, with a little prodding, to the narrative. A wider conflict between wings of the party, far less between Scottish Labour and London, is established for a backdrop.

But what happened in Falkirk? Perhaps those who say "we all know" could step forward and tell us. Even their favourite phrase, "vote-rigging scandal", is wide of the mark, but "alleged preparations for a possible attempt to rig a vote" doesn't have quite the same ring. We know only a few things for certain.

In June, on the basis of allegations, Labour in London suspended candidate and Unite member Karie Murphy along with the Falkirk party chairman Stephen Deans. In July, Ed Miliband called in the cops and denounced behaviour he refused to tolerate. Subsequently, however, the police failed to make any progress.

Undeterred, Mr Miliband proceeded to use the Falkirk "scandal" as a prime reason to launch an attempt to reform the Labour-union link. Platoons of superannuated Blairites, aware that Unite was working to support sympathetic candidates across Britain, rushed to agree. In September, nevertheless, the party was obliged to admit that neither Ms Murphy nor Mr Deans was guilty of wrongdoing. Both were reinstated.

That could have been the end of it. Mr Miliband could have swallowed a small humiliation and, with relief, moved on. But the party's suggestion that "key evidence" had been "withdrawn" was enough, for several observers, to keep the affair alive. Ineos, the Grangemouth operators, had meanwhile decided to believe that Mr Deans, a union convenor at the site, was guilty of using his time inappropriately. This became a handy excuse for an all-out assault on workers' wages, jobs and pensions.

Today, instead of the 100 or so new-minted Labour members at the start of the affair, attention falls on one couple, Michael and Lorraine Kane, and on emails held by Ineos. Did Lorraine Kane give a sworn statement, withdraw it and then reaffirm her claims? The first and last of these are not in question. But which claims? Do the emails reveal Unite's people wrote a "retraction letter"? So alleges The Sunday Times.

But Labour in London have spoken this week to Mrs Kane. The party says there are no grounds for a fresh inquiry because she stands by her sworn affidavit. Like the rest of us, she'd like to know what those emails contain. She wants equivalent information from other parties to the controversy. The rest of us would like to know how she and her husband "did not withdraw anything" yet reaffirm their original statements.

If an allegation was not withdrawn, why no fresh party inquiry? If Mrs Kane never intended to claim in her affidavit that wrongdoing occurred in the Falkirk selection, where did the fuss originate? If someone is suggesting she was in some manner persuaded or managed - the email trail, in other words - they had better come up with the goods.

One suspicion is that Labour, having botched one inquiry, do not want to return to the mess. Another notion, favoured by the Tories, runs that Mr Miliband is no longer in any mood to pick a fight with Unite and its general secretary, Len McCluskey. There is always a third thought: evidence for serious allegations is proving hard to come by.

Those emails might have the union bang to rights. That would suit Ineos. If a variety of personation was taking place during the selection battle, in any case, that would be a matter for the law and a serious blow to Unite. Once again, the police are involved. What's curious, though, is the extent to which Labour in Scotland and Labour in London are out of step.

Alistair Darling, the former Chancellor, says there has to be "a very thorough investigation". If the police proceed "there needs to be a full inquiry and I am quite clear that the results have to be published because that is the only way in which people will be satisfied that justice is done and been seen to be done". But London, having first claimed that the Kane evidence was withdrawn, is refusing to contemplate any such thing. Yesterday, Mr Miliband endorsed that decision. Johann Lamont, with the title of Scottish Labour leader, struggles to say what she thinks. This has not been her favourite year. She concedes that her party "should look at" a fresh investigation, but attempts to square the circle by denying that any report must be published. The swamp waters are up to her chin.

All the Labour people mentioned have claimed to know what went on in Falkirk. Each has deplored supposed outrages in the strongest terms. There has been a great deal of talk about "the facts". The largest fact is that the party is all over the shop, unable to agree even on the need to re-investigate, the quality of the evidence, or the need to publish. Motives are, to put it kindly, opaque.

What happened in Falkirk? Complaints were made. What has become of those complaints? Thus far, nothing much. Is there more to come? Those who say they know what happened would have you believe it. Those emails will need to be pretty conclusive. For now, we are offered slim pickings. This is odd in itself. Or perhaps not so odd.

As Unite and Mr McCluskey never tire of complaining, no row ever commences when Labour in London impose some fresh-from-Oxbridge special adviser on a hapless constituency party up north. That process just happens, magically, without lurid allegations of manipulation. If the union overstepped all bounds in Falkirk, it will deserve to pay. Someone had better prove the charges first.