DonkeySkin
You've walked right into the reason why it's considered a last resort to take things to court, especially when arguing a case that hasn't had similar cases like it before the Courts before. Essentially, as soon as a court makes a decision, at a very minimum that decision becomes part of the case law that then guides and informs all other similar cases that appear before the court. On the Civil side of the law you then have to take into account the type of Court making the decision. A case like this would be heard at the High Court, which means that not only would the decision create case law, it would also create judicial precedence, meaning that the judgement made would have to be made by all lower courts in similar cases and, with a few exceptions, would also be binding on the High Court itself.
But say somebody takes the risk and gets a court judgement that works for them. Well, enter the counterpart to the Judiciary - the Legislature (on a lower level the National Legislative Bodies, and then Westminster Parliament as a whole). It's another constitutional principle that Parliament is sovereign, meaning that, in theory, it can pass any legislation it likes and the Judiciary has no choice but to enforce it. (In practice the system is actually slightly more balanced than that, in part as being part of the European Court system but also, as this Government has found out, if the courts have ruled directly against the Government and the Government then gets Parliament to change the law solely to evade the court's judgement, then the Court will slap the Government down and call what they've done is illegal, (but that's really rare)). So, by and large, Parliament can pass any legislation it likes, and it has been known to get a statute passed in a day, so we're in situation where the laws that we live by, and the definitions that surround concepts within statute, can changed at any point for any reason. So, if the courts pass a judgement that a current or future Government decides doesn't suit its public policy then the Government can just bring in legislation changing the law and can do so surprisingly quickly.
And this is why trying to obtain a legal definition of concepts that we tend to take for granted (as opposed to seeking a clarification of an existing point of law) is generally considered futile. It doesn't matter what definition is made in statute because it's a definition written in sand and can just as easily be washed away with the next tide, and although the legal side of things thrives on exact definitions, the definitions are as narrowly tied to the case as it's possible to make because that way any statutory change to the definition has as much of a minimum impact as possible on the body of case law.