Does the British monarchy still exist in Wing Commander's 27th Century? It's not directly stated but it is implied by the "sir" in Admiral Tolwyn's formal title. As seen on office doors in Wing Commander II:
He thought for a moment of a distant ancestor of long ago, who, when contemplating the invasion and destruction of England, announced that even if England fell, the Empire, and with it the fleet, would still continue the fight. England. No, he didn't want to think of that now. ...
But it was the simple truth: the actual existence of his entire species rested in their hands. One wrong move on his part and it might all be over with. All of it gone forever, two thousand years of England gone, a cold silence of death, of extinction.
... think about that. The only bright spot was that for some reason the Cats had not launched a wave of strontium clad thermonukes. England had been spared as well, though it seemed at the moment to be an almost selfish thing to think about.