A king air is not a machine you can just jump into, straight from "normal" PPL flying.
It is big, heavy, fast and complex. Compared to a 73 it isn't difficult, but compare it to most PPL available a/c it is in a different league.
As has been pointed out before, larger a/c aren't more difficult to fly, but they are totally different to operate safely. With the lax attitude most have to reading the POH in something like a PA28, then I shudder to think of the same attitude being applied to something like B200.
It's not impossible by any means, but it is improbable, certainly in JAR land.
A type rating on a king air in the U.K is around £12K I think.