How does Williamson look himself in the mirror? He knows that he hasn't got his Knighthood through genuine means, or his ability like so many people who do get this honour for incredible acts of generosity, kindness, valour etc. He's got it because he has seen a couple of things that he shouldn't have and has promised he won't spill the beans.
It must be so bloody embarrassing, for him and even his family?! But of course so many of these people are "unembarrassable". (is that a word? Probably not, but it works in this context)