Good blogpost here on why Jeremy Corbyn should be applauded for not singing the national anthem - he'd have been a hypocrite to do so, he showed all the respect appropriate to the occasion anyway (which is more than some of the singers did), and thirdly, it's a lousy and absurd anthem anyway.
The real debate, of course, ought to be why we can't have an anthem that isn't offensive to Scots, Catholics and republicans, but I don't suppose we'll have that any time soon. The right-wing press, who have generally had a strange way of showing how much they respect the monarchy in the past, have their own very obvious agenda here. Incidentally, I wonder how many of their 'journalists' and photographers were singing? I wonder, too, how many of those who have criticised Corbyn could sing the anthem in its entirety?