Should I still go for an undergrad law degree here?
Or hope to do some sort of post-grad law degree overseas (think UK/US)?
A sad but unavoidable aspect of law is that formal practice is compartmentalized by jurisdiction. In short, to be admitted to practice in a certain country, you really should attend law school there.
That's not to say that it hasn't been done. People have done an undergrad LLB here and then sometime down the line gone to do a grad LLB/JD in US/Canada/UK (I don't know what the story is with HK). Nothing stops you from having multiple law degrees from different jurisdictions; in fact it is highly marketable in commercial law. It's slightly easier in common law countries as you may receive some credits for units you've done here. This can end up being very expensive, but hey, I've seen people blow more on cars.
Also, recently Australian law school have introduced dual law degree programs with partner law schools. I know that Monash has a 3-4 year 'dual JD', where you do part here and part at Washington College of Law. In the end you receive two JD's and can be admitted to practice in US and Australia (having fulfilled bar exam or PLT requirements). This appears to be a very selective program though.
I've heard of work arounds to, eg Canada has equivalence exams (12 of them apparently). This doesn't end up looking like a better option, as they are spaced so that they take a number of years to complete anyway, are expensive to sit, and failure rates are high.
So, yeah you can do it, but its not easy. I'd advice you not to do a law degree here, if you don't intend on using it here at some point.