Such examples can be found all over UK law, it is, as you say in effect a by-product of the common law system.
But also it also comes from the way legislation is written in the UK...
1. A member of parliament (MP) brings a "bill" to Parliament proposing a new law or a chnge in the law.
2. If it has legs, then it will end up being debated in Parliament
3. Almost always politics starts coming into play and MPs of all parties will usually propose real or party-political amendements to the bill which are then debated and voted on.
4. You then have a ping-pong process with the upper house (Lords), stuff goes back and forth between Lords and Commons ... more amendements are made along the way.
5. Finally once everyone has come to some sort of agreement it goes to the monarch to be signed into law (this is purely ceremonial, the document is presented to the monarch as a done-deal).
So that's why you end up with all these messy looking and almost incomprehensible pieces of legislation, there's quite a lot of "too many chefs" going on at every stage apart from the first and last.
Therefore as you point out it looking at UK law in the absence of case law is a fool's errand.
It is also where good barristers are worth their money because they are know the case-law like the back of their hand, and if there is no case law for your situation, they will have a good handle on the "letter and spirit" of the law in question and hence your prospects if it goes to court.
But also it also comes from the way legislation is written in the UK...
So that's why you end up with all these messy looking and almost incomprehensible pieces of legislation, there's quite a lot of "too many chefs" going on at every stage apart from the first and last.Therefore as you point out it looking at UK law in the absence of case law is a fool's errand.
It is also where good barristers are worth their money because they are know the case-law like the back of their hand, and if there is no case law for your situation, they will have a good handle on the "letter and spirit" of the law in question and hence your prospects if it goes to court.