Meeting with an old BA mate some years ago, and giving him a bit of a stir about the long sleeve Nigel's calling fully ready on the HongKong delivery freq, he explained it was, as Max Reheat indicated all LHR's fault.
He said over the years it had become the norm that pre ACARS PDC, when Nigel et al were ready to receive their departure clearance, they would call "Ready". They would then receive and read back their ATC clearance, and whilst not always told by LHR delivery to call back when "Fully Ready", both ATC and Nigel understood that when they were finally fully completely and awesomely ready for push back, a "Fully Ready" call was made and Nigel was sent to Ground/Ramp to request pushback of "THE Speedbird".
Unfortunately, such unnecessary verbiage has spread, and we now hear people crapping on like that in this part of the world too.