The UK changed to hPA to get in line with the rest of europe who has used hPA for years (or so I'm told).
The UK climb/descent phraseology is
"Descend flight level seven-zero"
"Descend to altitude four-thousand feet [QNH "number" [hectopascals]]"
Whereas I believe ICAO uses
"Descend to flight level seven zero"
"descend to four-thousand feet [QNH "number"]"
The UK uses the word "altitude" to make sure something like two "garbel" thousand is not misunderstood (garbel being say "five"). Instad you would in the UK get
"Descend to altitude "garbel" feet", which should make it clear the transmission was unreadable.
The removal of "to" before flight-levels is to further differentiate between an altitude and a flight level.
I prefer the UK way personally, but some would say I am biased