I use it from my time operating radios in the army cadets (otherwise known as "signals")
In the military, the phrase "repeat" is an artillery command, so if you missed what someone said on the radio you say "say again, over". That's the only reason, nothing to do with Thatcher.

Oh, and "over and out" is a nonsense.
( emvee cruor deo cruoris, Sat 3 May 2008, 13:41, Reply)