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How do I add the HS2 Snake Grid Projection to QGIS?

I have the projection file HS2TN15_NTv2.GSB and I have added to the shared projections folder C:\Program Files\QGIS 3.10\share\proj.

I also know that the HS2 survey grid is on the ESPG:9300 .

I know from the manual section 10.5.1 that I also need to add a custom projection, and include the parameters, part of which is the file name. But, being right at the limit of my knowledge I have no clue as to what this might comprise.

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HS2 Survey Grid NTv2 User Guide specifies the following coordinate system parameters in WKT format:

PROJCS["HS2_Snake",
  GEOGCS["GCS_HS2SD",
    DATUM["D_HS2SD",
      SPHEROID["WGS_1984", 6378137.0, 298.257223563]],
      PRIMEM["Greenwich", 0.0],
      UNIT["Degree", 0.0174532925199433]],
  PROJECTION["Transverse_Mercator"],
    PARAMETER["False_Easting", 198873.0046],
    PARAMETER["False_Northing", 375064.3871],
    PARAMETER["Central_Meridian", -1.5],
    PARAMETER["Scale_Factor", 1.0],
    PARAMETER["Latitude_Of_Origin", 52.3],
    UNIT["Meter", 1.0]]

For the proj string, including the nadgrids it would be:

+proj=tmerc +lat_0=52.3 +lon_0=-1.5 +k=1 +x_0=198873.0046 +y_0=375064.3871 +ellps=WGS84 +units=m +no_defs  +nadgrids=HS2TN15_NTv2.gsb

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