MML07 Grid - EPSG:9373

WKT

PROJCS["MML07_Grid", 
	GEOGCS["MML07-IRF", 
		DATUM["MML07_Intermediate_Reference_Frame", 
			SPHEROID["GRS_1980", 6378137.0, 298.257222101]], 
		PRIMEM["Greenwich", 0.0], 
		UNIT["Degree", 0.0174532925199433]], 
	PROJECTION["Transverse_Mercator"], 
	PARAMETER["False_Easting", 49350.157], 
	PARAMETER["False_Northing", 108398.212], 
	PARAMETER["Central_Meridian", -0.85], 
	PARAMETER["Scale_Factor", 1.0], 
	PARAMETER["Latitude_Of_Origin", 52.45], 
	UNIT["Meter", 1.0]]

WKT2

PROJCRS["MML07_Grid", 
	BASEGEOGCRS["MML07-IRF", 
		DATUM["MML07_Intermediate_Reference_Frame", 
			ELLIPSOID["GRS_1980", 6378137.0, 298.257222101]], 
		PRIMEM["Greenwich", 0.0], 
		CS[ellipsoidal, 2], 
		AXIS["Latitude (lat)", north, 
			ORDER[1]], 
		AXIS["Longitude (lon)", east, 
			ORDER[2]], 
		ANGLEUNIT["Degree", 0.0174532925199433]], 
	CONVERSION["Transverse_Mercator", 
		METHOD["Transverse_Mercator"], 
		PARAMETER["False_Easting", 49350.157], 
		PARAMETER["False_Northing", 108398.212], 
		PARAMETER["Central_Meridian", -0.85], 
		PARAMETER["Scale_Factor", 1.0], 
		PARAMETER["Latitude_Of_Origin", 52.45]], 
	CS[Cartesian, 2], 
	AXIS["Easting (X)", east, 
		ORDER[1]], 
	AXIS["Northing (Y)", north, 
		ORDER[2]], 
	LENGTHUNIT["Meter", 1.0], 
	ID["EPSG", "9373"]]

Data from @esri/proj-codes

{
  "wkid": 9373,
  "latestWkid": 9373,
  "gcsWkid": 9372,
  "macro": "PE_PCS_MML07_GRID",
  "name": "MML07_Grid",
  "wkt": "PROJCS[\"MML07_Grid\",GEOGCS[\"MML07-IRF\",DATUM[\"MML07_Intermediate_Reference_Frame\",SPHEROID[\"GRS_1980\",6378137.0,298.257222101]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",49350.157],PARAMETER[\"False_Northing\",108398.212],PARAMETER[\"Central_Meridian\",-0.85],PARAMETER[\"Scale_Factor\",1.0],PARAMETER[\"Latitude_Of_Origin\",52.45],UNIT[\"Meter\",1.0]]",
  "wkt2": "PROJCRS[\"MML07_Grid\",BASEGEOGCRS[\"MML07-IRF\",DATUM[\"MML07_Intermediate_Reference_Frame\",ELLIPSOID[\"GRS_1980\",6378137.0,298.257222101]],PRIMEM[\"Greenwich\",0.0],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433]],CONVERSION[\"Transverse_Mercator\",METHOD[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",49350.157],PARAMETER[\"False_Northing\",108398.212],PARAMETER[\"Central_Meridian\",-0.85],PARAMETER[\"Scale_Factor\",1.0],PARAMETER[\"Latitude_Of_Origin\",52.45]],CS[Cartesian,2],AXIS[\"Easting (X)\",east,ORDER[1]],AXIS[\"Northing (Y)\",north,ORDER[2]],LENGTHUNIT[\"Meter\",1.0],ID[\"EPSG\",\"9373\"]]",
  "description": "MML07 Grid",
  "authority": "EPSG",
  "version": "9.8.12(12.8.0)",
  "deprecated": "no",
  "areaname": "UK - London to Sheffield",
  "extent": {
    "slat": 51.46,
    "nlat": 53.42,
    "llon": -1.89,
    "rlon": 0.16
  }
}