The CAA, against much opposition, decided a couple of years ago to implement this as it is the ICAO 'standard', otherwise it's exactly the same unit.
Pilots don't like it, controllers and FISOs don't like it, but the CAA insist on using it even though it makes RTF more complex as it doesn't 'roll off the tongue' like 'millibars'.
There is a possibility it may officially be abbreviated sometime in the future but the decision has yet to be made on this.