diff --git a/.upgradenotes/MDL-83703-2024111301454058.yml b/.upgradenotes/MDL-83703-2024111301454058.yml
new file mode 100644
index 00000000000..b2f12587c63
--- /dev/null
+++ b/.upgradenotes/MDL-83703-2024111301454058.yml
@@ -0,0 +1,7 @@
+issueNumber: MDL-83703
+notes:
+  core:
+    - message: >
+        Support for `subplugins.php` files has been removed. All subplugin
+        metadata must be created in a `subplugins.json` file.
+      type: removed
diff --git a/admin/tool/mfa/db/subplugins.php b/admin/tool/mfa/db/subplugins.php
deleted file mode 100644
index 68a0cc3e40e..00000000000
--- a/admin/tool/mfa/db/subplugins.php
+++ /dev/null
@@ -1,28 +0,0 @@
-<?php
-// This file is part of Moodle - http://moodle.org/
-//
-// Moodle is free software: you can redistribute it and/or modify
-// it under the terms of the GNU General Public License as published by
-// the Free Software Foundation, either version 3 of the License, or
-// (at your option) any later version.
-//
-// Moodle is distributed in the hope that it will be useful,
-// but WITHOUT ANY WARRANTY; without even the implied warranty of
-// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
-// GNU General Public License for more details.
-//
-// You should have received a copy of the GNU General Public License
-// along with Moodle.  If not, see <http://www.gnu.org/licenses/>.
-
-/**
- * Definition of MFA sub-plugins (factors).
- *
- * @package     tool_mfa
- * @author      Mikhail Golenkov <golenkovm@gmail.com>
- * @copyright   Catalyst IT
- * @license     http://www.gnu.org/copyleft/gpl.html GNU GPL v3 or later
- */
-
-defined('MOODLE_INTERNAL') || die();
-
-$subplugins = (array) json_decode(file_get_contents($CFG->dirroot."/admin/tool/mfa/db/subplugins.json"))->plugintypes;
diff --git a/lib/classes/component.php b/lib/classes/component.php
index 931e69c11e2..1b0d791b218 100644
--- a/lib/classes/component.php
+++ b/lib/classes/component.php
@@ -754,9 +754,10 @@ $cache = ' . var_export($cache, true) . ';
                 error_log("$ownerdir/db/subplugins.json is invalid ($jsonerror)");
             }
         } else if (file_exists("$ownerdir/db/subplugins.php")) {
-            error_log('Use of subplugins.php has been deprecated. ' .
-                "Please update your '$ownerdir' plugin to provide a subplugins.json file instead.");
-            include("$ownerdir/db/subplugins.php");
+            throw new coding_exception(
+                'Use of subplugins.php has been deprecated and is no longer supported. ' .
+                "Please update your '$ownerdir' plugin to provide a subplugins.json file instead.",
+            );
         }
 
         foreach ($subplugins as $subtype => $dir) {
diff --git a/lib/tests/component_test.php b/lib/tests/component_test.php
index b8825588c32..f29ba2e10cd 100644
--- a/lib/tests/component_test.php
+++ b/lib/tests/component_test.php
@@ -16,6 +16,7 @@
 
 namespace core;
 
+use core\exception\coding_exception;
 use DirectoryIterator;
 use ReflectionClass;
 use ReflectionProperty;
@@ -36,6 +37,7 @@ final class component_test extends \advanced_testcase {
         parent::tearDown();
 
         component::reset();
+        ini_set('error_log', null);
     }
 
     /**
@@ -1382,4 +1384,147 @@ final class component_test extends \advanced_testcase {
             }
         }
     }
+
+    /**
+     * Test that fetching of subtype data throws an exception when a subplugins.php is present without a json equivalent.
+     */
+    public function test_fetch_subtypes_php_only(): void {
+        $vfileroot = \org\bovigo\vfs\vfsStream::setup('root', null, [
+            'plugintype' => [
+                'exampleplugin' => [
+                    'db' => [
+                        'subplugins.php' => '',
+                    ],
+                ],
+            ],
+        ]);
+
+        $this->expectException(coding_exception::class);
+        $this->expectExceptionMessageMatches('/Use of subplugins.php has been deprecated and is no longer supported/');
+
+        $pluginroot = $vfileroot->getChild('plugintype/exampleplugin');
+
+        $rcm = new \ReflectionMethod(\core\component::class, 'fetch_subtypes');
+        $rcm->invoke(null, $pluginroot->url());
+    }
+
+    /**
+     * Test that fetching of subtype data does not throw an exception when a subplugins.php is present
+     * with a json file equivalent.
+     *
+     * Note: The content of the php file is irrelevant and we no longer use it anyway.
+     */
+    public function test_fetch_subtypes_php_and_json(): void {
+        global $CFG;
+
+        $this->resetAfterTest();
+        $vfileroot = \org\bovigo\vfs\vfsStream::setup('root', null, [
+            'plugintype' => [
+                'exampleplugin' => [
+                    'db' => [
+                        'subplugins.json' => json_encode([
+                            'plugintypes' => [
+                                'exampleplugina' => 'plugintype/exampleplugin/apples',
+                            ],
+                        ]),
+                        'subplugins.php' => '',
+                    ],
+                    'apples' => [],
+                ],
+            ],
+        ]);
+
+        $CFG->dirroot = $vfileroot->url();
+        $pluginroot = $vfileroot->getChild('plugintype/exampleplugin');
+
+        $rcm = new \ReflectionMethod(\core\component::class, 'fetch_subtypes');
+        $subplugins = $rcm->invoke(null, $pluginroot->url());
+
+        $this->assertEquals([
+            'exampleplugina' => $pluginroot->getChild('apples')->url(),
+        ], $subplugins);
+    }
+
+    /**
+     * Test that fetching of subtype data throws appropriate exceptions when a subplugins.php is present
+     * with a json file equivalent.
+     *
+     * Note: The content of the php file is irrelevant and we no longer use it anyway.
+     *
+     * @dataProvider invalid_subplugins_json_provider
+     * @param string[] $expectedwarnings Errors to expect in the exception message
+     * @param array[] $plugintypesdir The contents of the subplugins.json file
+     */
+    public function test_fetch_subtypes_json_invalid_values(
+        array $expectedwarnings,
+        array $plugintypesdir,
+    ): void {
+        global $CFG;
+
+        $this->resetAfterTest();
+        $vfileroot = \org\bovigo\vfs\vfsStream::setup('root', null, [
+            'plugintype' => [
+                'exampleplugin' => [
+                    'db' => [
+                        'subplugins.json' => json_encode([
+                            'plugintypes' => $plugintypesdir,
+                        ]),
+                        'subplugins.php' => '',
+                    ],
+                    'apples' => [],
+                ],
+            ],
+        ]);
+
+        $CFG->dirroot = $vfileroot->url();
+        $pluginroot = $vfileroot->getChild('plugintype/exampleplugin');
+
+        $logdir = make_request_directory();
+        $logfile = "{$logdir}/error.log";
+        ini_set('error_log', $logfile);
+
+        $rcm = new \ReflectionMethod(\core\component::class, 'fetch_subtypes');
+        $rcm->invoke(null, $pluginroot->url());
+
+        $warnings = file_get_contents($logfile);
+        foreach ($expectedwarnings as $expectedwarning) {
+            $this->assertMatchesRegularExpression($expectedwarning, $warnings);
+        }
+    }
+
+    /**
+     * Data provider for invalid subplugins.json files.
+     *
+     * @return array
+     */
+    public static function invalid_subplugins_json_provider(): array {
+        return [
+            'Invalid characters in subtype name' => [
+                'expectedwarnings' => [
+                    "/Invalid subtype .*APPLES.*detected.*invalid characters present/",
+                ],
+                'plugintypesdir' => [
+                    'APPLES' => 'plugintype/exampleplugin/APPLES',
+                ],
+            ],
+
+            'Subplugin which duplicates a core subsystem' => [
+                'expectedwarnings' => [
+                    "/Invalid subtype .*editor.*detected.*duplicates core subsystem/",
+                ],
+                'plugintypesdir' => [
+                    'editor' => 'plugintype/exampleplugin/apples',
+                ],
+            ],
+
+            'Subplugin directory does not exist' => [
+                'expectedwarnings' => [
+                    "/Invalid subtype directory/",
+                ],
+                'plugintypesdir' => [
+                    'exampleapples' => 'plugintype/exampleplugin/pears',
+                ],
+            ],
+        ];
+    }
 }