Mark Thatcher is quite successful because he shamelessly traded on his mummy's name in an arms deal with the Saudis. Not that it was his idea, of course, but some wealthy men with genuine entrepreneurial skills saw him as a useful conduit with connections and groomed him for the job. Later he married a Texan heiress, falling ass-backwards into money.

So there you have it. To be rich, you neeed no mad skillz. Just make sure you are the son of the Prime Minister and then marry a wealthy heiress. Easy.