Law is extremely complex and no one single person can be expected to memorise and know all of it, for the simple reason it often changes - not only in terms of new acts, but also High Court rulings, etc. There's a reason why top lawyers will specialise in a certain aspect of law, heck some lawyers will only take on cases of a certain, specific crime, e.g. Drink Drive lawyers.
Unfortunately finding what the law is isn't as simple as Googling. An Act may say something, but it could be that a High Court ruling has decided it means something else, for example. For drink driving, for example, there's a huge load of paperwork that can needs to be accurately completed for a conviction to stand.
This is precisely why the Police arrest "on suspicion"
The policeman needs a lesson in using the internet, that's for the sure.