I am wondering myself about the exact details of their nature. They exist for sure. rather than physically shapeshifting, and this is what I believe Icke is trying to say, they may have the ability to impress on your mind their looks which are in fact different.

Then another source, Canadian song writer and showbiz insider Donald Marshall, has written a whole lot about them, stating they can prolong their life by taking over a human body, as a parasite. A small worm that injects itself into human brain via eye. He calls those people "hosts". So that would be your lizard people in the government I guess.

His material is rather fascinating, you should read it.