To me that sounds quite weird. As long as you stay in the circuit, I SUPPOSE it is OK, but outside the circuit I would consider that an unnecessary source of possible conflict. From a quick review on the internet it seems that this is to a certain extent a holdover from the past and that current wisdom in the UK also favours QNH.
FWIW I did all my IRL flying many years ago in South Africa and there is was - like apparently most places in the world - QNH only.
And BTW the SI unit of measure for pressure is hectopascal (hPa). Even though it is essentially the same thing, I believe the term millibar is no longer officially correct.