Let me correct myself.
The most recent transformation is OSTN15. OSTN15, in combination with the ETRS89 coordinates of the OS Net stations, define the National Grid since August, 2016.
OSTN15 transformation is available in ArcGIS and it’s possible to work with it in QGIS.
In ReachView 3 beta, the OSTN15 transformation is now available. We’ll add the OSGM15 geoid shortly. Please make sure that during the survey you set the base coordinates in ETRS89.