Now it is unlikely Anderton will stand in 2011, but most people have thought it is not likely he will make a retirement announcement as early as 2009, as that makes him fairly irrelevant for the rest of the parliamentary term. Late 2010 is when you expect MPs to generally signal their intentions.

So for the last few months the MP.Anderton stock has been at around 25c – reflecting a 25% probability that he may announce this year.

But around a fortnight ago, one or more people started buying up MP.Anderton stock. And steadily over the fortnight it has shot up to almost 60c, or 60%.

I find it almost impossible to believe this is normal movement – especially considering Anderton has made no public indications. This suggests to me that someone with inside knowledge is buying up large to try and make a killing. That is legal incidentially as the idea of a prediction market is to get insider information out into the public.

So based on the movement in the share price, the only logical explanation is that Anderton has let it be known he will announce his retirement this year. It may even be Anderton who is buying up the shares?