It might not be directly related. The Australian Tax Office went after this guy. The first case against a gambler.I spoke at length about this about 3 years ago with 2 colleagues whom are in the legal profession.
Simply put - they would happily take any client on and defend them in any case brought against their client if "gambling" was the term used and always had been used in defining their ability to obtain income.
They went on to add:
Find just one case where a high earning individual has been forced to pay taxation on spread betting income. Just one
who then moved his business to the Isle of Man
If you are big enough, the tax office will come after you. If there are no cases in the UK it just mean that there are no worthwhile targets.