Let me answer your points Jim.

"So neither (Republic or Britain) have a say on the question because it would not produce the resuly required - is that right?

YES! RIGHT! The "required" result is the one wanted by the people of NI themselves, not imposed by outsiders.

"...decision should rest solely with the people of the island of Ireland."
Absolutely - this is what I have been saying all along."

No, you have just added mainland voters too!

The US Civil War. YOU gave it as an analogy of how NI should be dealt with, and only today demanded I should respond to it.

"Straight question - should the British people have the right to a say in whether British troops are sent to Ireland or not?"

The British people, through their elected government, DO decide where troops are sent.