Why Gandhi sing "God save the king"?

I see no evidence of this in Orwell's, Reflections on Gandhi. One can infer, that Gandhi may have sung this in response to the fact India was a British colony, but he would have done this as a sign of respect.... not belief.

Because it was ostensibly to show respect to the British empire. But really to toy with the police men and get the police men in the room standing with them because police men are not allowed to sit during the national anthem under any circumstances. Gandhi cornered them.