HS2-IRF - EPSG:9299

WKT

GEOGCS["HS2-IRF", 
	DATUM["HS2_Intermediate_Reference_Frame", 
		SPHEROID["GRS_1980", 6378137.0, 298.257222101]], 
	PRIMEM["Greenwich", 0.0], 
	UNIT["Degree", 0.0174532925199433]]

WKT2

GEOGCRS["HS2-IRF", 
	DATUM["HS2_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], 
	ID["EPSG", "9299"]]

Data from @esri/proj-codes

{
  "wkid": 9299,
  "latestWkid": 9299,
  "macro": "PE_GCS_HS2_IRF",
  "name": "HS2-IRF",
  "wkt": "GEOGCS[\"HS2-IRF\",DATUM[\"HS2_Intermediate_Reference_Frame\",SPHEROID[\"GRS_1980\",6378137.0,298.257222101]],PRIMEM[\"Greenwich\",0.0],UNIT[\"Degree\",0.0174532925199433]]",
  "wkt2": "GEOGCRS[\"HS2-IRF\",DATUM[\"HS2_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],ID[\"EPSG\",\"9299\"]]",
  "description": "HS2-IRF",
  "authority": "EPSG",
  "version": "9.8.13(12.8.0)",
  "deprecated": "no",
  "areaname": "UK - London to Birmingham and Crewe",
  "extent": {
    "slat": 51.45,
    "nlat": 53.3,
    "llon": -2.75,
    "rlon": 0
  }
}