Avar;
Even if it were true that they had strayed into Iranian waters, do you believe for a second that armed Royal Marines would give themselves up willy-nilly? Did the Revolutionary Guard hail them with bullhorns and serve them with a Revolutionary arrest warrant? Get real.
Will most Americans, brown, black, white etc., etc, side with the British on this? You bet they will. Any Americans old enough to remember the Iranian hostage crisis will feel a certain resonance. And, by the way, Jimmy Carter isn't President any more. Were 15 US sailors in Iranian hands the steam would be coming out of the Pentagon right now. The only reason for keeping this low key is a recognition that this foolish move harms the Iranian cause internationally and likely strengthens moderates within Iran.
Here is hoping some cooler head in Iran steps in and slaps the Revolutioanry Guard upside the head.