I'm pretty sure you could also use GPS.ChangeDatum to do it.
It could but I think this library is more accurate as it uses a 7 parameter Helmert transformation (I don't really know what that means
but the source code contains the URL of the website that I obtained the code from that initially came from the OS documentation). It could even be a bit more accurate as the algorithm also includes ellipsoid height but I've set that to zero for convenience as it has a really minor effect below the levels at which aircraft fly. The library round trips from WSG84 through OSGB36 to National Grid and back with remarkable accuracy.
Actually the major feature of the library is the transformation to the OS National Grid Reference which is the primary way that map locations are specified in the UK. We don't use lat/long we use the National Grid and it is printed on all OS maps as a grid as the primary location mechanism. Lat/long is included but only as small crosses at spot points for cross reference to the grid.
EDIT:- I've done the comparison and the difference for locations near to me is about 3 metres in both directions between the 7 parameter Helmert transormation from the Ordnance Survey documentation and whatever the transformation implemented in the GPS Converter is. You've got to get the signs of the dx,dy and dz correct though!