I'm trying to save 2D data on a layer (currently to British National Grid co-ordinates) to an accurate KML version using QGIS 2.14.19 Essen. Saving directly to KML using the WGS84 CRS doesn't give an accurate result.
I have noted that accurate transformation needs to use the OSTN15_NTv2.gsb files provided by Ordnance Survey, together with an updated SRS database file - both of which I have saved down into the appropriate folders (as recommended here, for example, https://dragons8mycat.com/2016/09/26/add-ostn15-to-qgis-2-16/) but when I try to save the transformed data in QGIS (right click on the layer > Save as...) the OSTN15 CRS option isn't listed.
I have restarted QGIS etc. but I can't fathom how to try the file/coordinate system conversion using this transformation CRS.
Can anyone help, please?