Put them in jail for 5 or 10 years.
Saying that it's 'very serious' and they 'take it very seriously' does f*** all if they just end up with a slap on the wrist. They should at least be honest and say, ''we think this crime is a bit of a bummer if you're the one affected, but on the whole we don't care. We have bigger issues to deal with, such as telling the general public what kind of porn is OK to watch, making certain kinds of sketches and computer generated images illegal, and our current major problem is trying to figure out how to ban plastic bags (even though we can just make biodegradable ones mandatory).''
Private investigators working illegally can land the victim in a LOT of serious trouble. It should not be that easy to track people down and they should be looking into exactly how the investigator (any P.Is) managed to get this infomation illegally in the first place, and fine the hell out of them, possibly jailing them too.
You would be surprised the amount of information that will be given out without much trickery or effort on the investigator's behalf.
The fines for serious crimes should be at least £2000. I suggest around £10,000.
The person being fined should have it be a BURDEN. A punishment, something that they need to work for, that will be on their mind every day and seriously affect their lives - not something that they can pay with a month's wages or pocket money!!
What the hell is the point in lousy fines? It's even worse than doing nothing.
A lousy fine for the sake of looking like they took some sort of action is nothing but a slap in the face and a mockery of the law and peoples right to privacy.