It must be mind-bogglingly difficult for him at the moment. A lifetime of rebellion and sticking to his principles and now he simply has to conform, at least in some things - the suit and tie for instance is a small concession, but he's had to do it. Principles can be lofty but also hard to understand, and the general public will always sweat the small stuff because it's easy to do that.
I don't criticise him at all for not singing the national anthem because the words are all about the monarchy, not the country, and he is a committed republican. However, the tabloids will of course love the chance to say "he's disrespecting our war dead". Standing in silence isn't disrespectful.