EPSG:27700

PROJCRS["OSGB36 / British National Grid",
    BASEGEOGCRS["OSGB36",
        DATUM["Ordnance Survey of Great Britain 1936",
            ELLIPSOID["Airy 1830",6377563.396,299.3249646,
                LENGTHUNIT["metre",1]]],
        PRIMEM["Greenwich",0,
            ANGLEUNIT["degree",0.0174532925199433]],
        ID["EPSG",4277]],
    CONVERSION["British National Grid",
        METHOD["Transverse Mercator",
            ID["EPSG",9807]],
        PARAMETER["Latitude of natural origin",49,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8801]],
        PARAMETER["Longitude of natural origin",-2,
            ANGLEUNIT["degree",0.0174532925199433],
            ID["EPSG",8802]],
        PARAMETER["Scale factor at natural origin",0.9996012717,
            SCALEUNIT["unity",1],
            ID["EPSG",8805]],
        PARAMETER["False easting",400000,
            LENGTHUNIT["metre",1],
            ID["EPSG",8806]],
        PARAMETER["False northing",-100000,
            LENGTHUNIT["metre",1],
            ID["EPSG",8807]]],
    CS[Cartesian,2],
        AXIS["(E)",east,
            ORDER[1],
            LENGTHUNIT["metre",1]],
        AXIS["(N)",north,
            ORDER[2],
            LENGTHUNIT["metre",1]],
    USAGE[
        SCOPE["Engineering survey, topographic mapping."],
        AREA["United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore."],
        BBOX[49.75,-9.01,61.01,2.01]],
    ID["EPSG",27700]]

PROJCS["British_National_Grid",
    GEOGCS["GCS_OSGB_1936",
        DATUM["D_OSGB_1936",
            SPHEROID["Airy_1830",6377563.396,299.3249646],
            EXTENSION["PROJ4_GRIDS","uk_os_OSTN15_NTv2_OSGBtoETRS.tif"]],
        PRIMEM["Greenwich",0.0],
        UNIT["Degree",0.0174532925199433]],
    PROJECTION["Transverse_Mercator"],
    PARAMETER["False_Easting",400000.0],
    PARAMETER["False_Northing",-100000.0],
    PARAMETER["Central_Meridian",-2.0],
    PARAMETER["Scale_Factor",0.9996012717],
    PARAMETER["Latitude_Of_Origin",49.0],
    UNIT["Meter",1.0]]

proj4.defs("EPSG:27700","+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +nadgrids=uk_os_OSTN15_NTv2_OSGBtoETRS.tif +units=m +no_defs +type=crs");

{
    "$schema": "https://proj.org/schemas/v0.7/projjson.schema.json",
    "type": "ProjectedCRS",
    "name": "OSGB36 / British National Grid",
    "base_crs": {
        "name": "OSGB36",
        "datum": {
            "type": "GeodeticReferenceFrame",
            "name": "Ordnance Survey of Great Britain 1936",
            "ellipsoid": {
                "name": "Airy 1830",
                "semi_major_axis": 6377563.396,
                "inverse_flattening": 299.3249646
            }
        },
        "coordinate_system": {
            "subtype": "ellipsoidal",
            "axis": [
                {
                    "name": "Geodetic latitude",
                    "abbreviation": "Lat",
                    "direction": "north",
                    "unit": "degree"
                },
                {
                    "name": "Geodetic longitude",
                    "abbreviation": "Lon",
                    "direction": "east",
                    "unit": "degree"
                }
            ]
        },
        "id": {
            "authority": "EPSG",
            "code": 4277
        }
    },
    "conversion": {
        "name": "British National Grid",
        "method": {
            "name": "Transverse Mercator",
            "id": {
                "authority": "EPSG",
                "code": 9807
            }
        },
        "parameters": [
            {
                "name": "Latitude of natural origin",
                "value": 49,
                "unit": "degree",
                "id": {
                    "authority": "EPSG",
                    "code": 8801
                }
            },
            {
                "name": "Longitude of natural origin",
                "value": -2,
                "unit": "degree",
                "id": {
                    "authority": "EPSG",
                    "code": 8802
                }
            },
            {
                "name": "Scale factor at natural origin",
                "value": 0.9996012717,
                "unit": "unity",
                "id": {
                    "authority": "EPSG",
                    "code": 8805
                }
            },
            {
                "name": "False easting",
                "value": 400000,
                "unit": "metre",
                "id": {
                    "authority": "EPSG",
                    "code": 8806
                }
            },
            {
                "name": "False northing",
                "value": -100000,
                "unit": "metre",
                "id": {
                    "authority": "EPSG",
                    "code": 8807
                }
            }
        ]
    },
    "coordinate_system": {
        "subtype": "Cartesian",
        "axis": [
            {
                "name": "Easting",
                "abbreviation": "E",
                "direction": "east",
                "unit": "metre"
            },
            {
                "name": "Northing",
                "abbreviation": "N",
                "direction": "north",
                "unit": "metre"
            }
        ]
    },
    "scope": "Engineering survey, topographic mapping.",
    "area": "United Kingdom (UK) - offshore to boundary of UKCS within 49°45'N to 61°N and 9°W to 2°E; onshore Great Britain (England, Wales and Scotland). Isle of Man onshore.",
    "bbox": {
        "south_latitude": 49.75,
        "west_longitude": -9.01,
        "north_latitude": 61.01,
        "east_longitude": 2.01
    },
    "id": {
        "authority": "EPSG",
        "code": 27700
    }
}

<?xml version="1.0" encoding="utf-8"?>
<Map srs="+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +nadgrids=uk_os_OSTN15_NTv2_OSGBtoETRS.tif +units=m +no_defs +type=crs">
	<Layer srs="+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +nadgrids=uk_os_OSTN15_NTv2_OSGBtoETRS.tif +units=m +no_defs +type=crs">
	</Layer>
</Map>

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 27700, 'EPSG', 27700, '+proj=tmerc +lat_0=49 +lon_0=-2 +k=0.9996012717 +x_0=400000 +y_0=-100000 +ellps=airy +nadgrids=uk_os_OSTN15_NTv2_OSGBtoETRS.tif +units=m +no_defs +type=crs', 'PROJCS["OSGB36 / British National Grid",GEOGCS["OSGB36",DATUM["Ordnance_Survey_of_Great_Britain_1936",SPHEROID["Airy 1830",6377563.396,299.3249646],EXTENSION["PROJ4_GRIDS","uk_os_OSTN15_NTv2_OSGBtoETRS.tif"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.0174532925199433,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4277"]],PROJECTION["Transverse_Mercator"],PARAMETER["latitude_of_origin",49],PARAMETER["central_meridian",-2],PARAMETER["scale_factor",0.9996012717],PARAMETER["false_easting",400000],PARAMETER["false_northing",-100000],UNIT["metre",1,AUTHORITY["EPSG","9001"]],AXIS["Easting",EAST],AXIS["Northing",NORTH],AUTHORITY["EPSG","27700"]]');