diff --git a/lib/editor/atto/plugins/managefiles/lang/en/atto_managefiles.php b/lib/editor/atto/plugins/managefiles/lang/en/atto_managefiles.php
index 53db50bd918..f98243e0191 100644
--- a/lib/editor/atto/plugins/managefiles/lang/en/atto_managefiles.php
+++ b/lib/editor/atto/plugins/managefiles/lang/en/atto_managefiles.php
@@ -29,4 +29,5 @@ $string['managefiles'] = 'Manage files';
 $string['missingfiles'] = 'Missing files';
 $string['pluginname'] = 'Manage files';
 $string['unusedfilesdesc'] = 'The following embedded files are not used in the text area:';
+$string['unusedfilesremovalnotice'] = 'Any unused files will be automatically deleted when saving changes.';
 $string['unusedfilesheader'] = 'Unused files';
diff --git a/lib/editor/atto/plugins/managefiles/lib.php b/lib/editor/atto/plugins/managefiles/lib.php
index bce1bd469fe..b6ff2a1a259 100644
--- a/lib/editor/atto/plugins/managefiles/lib.php
+++ b/lib/editor/atto/plugins/managefiles/lib.php
@@ -55,7 +55,8 @@ function atto_managefiles_params_for_js($elementid, $options, $fpoptions) {
 
     if (!$disabled) {
         $params['usercontext'] = context_user::instance($USER->id)->id;
-        foreach (array('itemid', 'context', 'areamaxbytes', 'maxbytes', 'subdirs', 'return_types') as $key) {
+        foreach (array('itemid', 'context', 'areamaxbytes', 'maxbytes', 'subdirs', 'return_types',
+                       'removeorphaneddrafts') as $key) {
             if (isset($options[$key])) {
                 if ($key === 'context' && is_object($options[$key])) {
                     // Just context id is enough.
diff --git a/lib/editor/atto/plugins/managefiles/manage.php b/lib/editor/atto/plugins/managefiles/manage.php
index ff6922bdf56..5dd39a49481 100644
--- a/lib/editor/atto/plugins/managefiles/manage.php
+++ b/lib/editor/atto/plugins/managefiles/manage.php
@@ -35,6 +35,7 @@ $return_types = optional_param('return_types', null, PARAM_INT);
 $areamaxbytes = optional_param('areamaxbytes', FILE_AREA_MAX_BYTES_UNLIMITED, PARAM_INT);
 $contextid = optional_param('context', SYSCONTEXTID, PARAM_INT);
 $elementid = optional_param('elementid', '', PARAM_TEXT);
+$removeorphaneddrafts = optional_param('removeorphaneddrafts', 0, PARAM_INT);
 
 $context = context::instance_by_id($contextid);
 if ($context->contextlevel == CONTEXT_MODULE) {
@@ -75,7 +76,7 @@ $options = array(
     'accepted_types' => $accepted_types,
     'areamaxbytes' => $areamaxbytes,
     'return_types' => $return_types,
-    'context' => $context,
+    'context' => $context
 );
 
 $usercontext = context_user::instance($USER->id);
@@ -87,8 +88,8 @@ foreach ($files as $file) {
 }
 
 $mform = new atto_managefiles_manage_form(null,
-    array('options' => $options, 'draftitemid' => $itemid, 'files' => $filenames, 'elementid' => $elementid),
-    'post', '', array('id' => 'atto_managefiles_manageform'));
+    array('options' => $options, 'draftitemid' => $itemid, 'files' => $filenames, 'elementid' => $elementid,
+        'removeorphaneddrafts' => $removeorphaneddrafts), 'post', '', array('id' => 'atto_managefiles_manageform'));
 
 if ($data = $mform->get_data()) {
     if (!empty($data->deletefile)) {
diff --git a/lib/editor/atto/plugins/managefiles/manage_form.php b/lib/editor/atto/plugins/managefiles/manage_form.php
index 50bb8dd5dfa..a5569aa92a5 100644
--- a/lib/editor/atto/plugins/managefiles/manage_form.php
+++ b/lib/editor/atto/plugins/managefiles/manage_form.php
@@ -47,6 +47,7 @@ class atto_managefiles_manage_form extends moodleform {
         $elementid = $this->_customdata['elementid'];
         $options = $this->_customdata['options'];
         $files = $this->_customdata['files'];
+        $removeorphaneddrafts = $this->_customdata['removeorphaneddrafts'];
 
         $mform->addElement('header', 'filemanagerhdr', get_string('filemanager', 'atto_managefiles'));
 
@@ -69,6 +70,12 @@ class atto_managefiles_manage_form extends moodleform {
 
         $mform->addElement('filemanager', 'files_filemanager', '', null, $options);
 
+        // Let the user know that any drafts not referenced in the text will be removed automatically.
+        if ($removeorphaneddrafts) {
+            $mform->addElement('static', '', '',
+                html_writer::tag('div', get_string('unusedfilesremovalnotice', 'atto_managefiles')));
+        }
+
         $mform->addElement('header', 'missingfileshdr', get_string('missingfiles', 'atto_managefiles'));
         $mform->addElement('static', '', '',
             html_writer::tag('div',
diff --git a/lib/filelib.php b/lib/filelib.php
index d2779ced516..4b74d41e7a7 100644
--- a/lib/filelib.php
+++ b/lib/filelib.php
@@ -237,6 +237,9 @@ function file_postupdate_standard_editor($data, $field, array $options, $context
     if (!isset($options['maxbytes'])) {
         $options['maxbytes'] = 0; // unlimited
     }
+    if (!isset($options['removeorphaneddrafts'])) {
+        $options['removeorphaneddrafts'] = false; // Don't remove orphaned draft files by default.
+    }
 
     if ($options['trusttext']) {
         $data->{$field.'trust'} = trusttext_trusted($context);
@@ -249,6 +252,10 @@ function file_postupdate_standard_editor($data, $field, array $options, $context
     if ($options['maxfiles'] == 0 or is_null($filearea) or is_null($itemid) or empty($editor['itemid'])) {
         $data->{$field} = $editor['text'];
     } else {
+        // Clean the user drafts area of any files not referenced in the editor text.
+        if ($options['removeorphaneddrafts']) {
+            file_remove_editor_orphaned_files($editor);
+        }
         $data->{$field} = file_save_draft_area_files($editor['itemid'], $context->id, $component, $filearea, $itemid, $options, $editor['text'], $options['forcehttps']);
     }
     $data->{$field.'format'} = $editor['format'];
@@ -792,6 +799,38 @@ function file_restore_source_field_from_draft_file($storedfile) {
     }
     return $storedfile;
 }
+
+/**
+ * Removes those files from the user drafts filearea which are not referenced in the editor text.
+ *
+ * @param stdClass $editor The online text editor element from the submitted form data.
+ */
+function file_remove_editor_orphaned_files($editor) {
+    global $CFG, $USER;
+
+    // Find those draft files included in the text, and generate their hashes.
+    $context = context_user::instance($USER->id);
+    $baseurl = $CFG->wwwroot . '/draftfile.php/' . $context->id . '/user/draft/' . $editor['itemid'] . '/';
+    $pattern = "/" . preg_quote($baseurl, '/') . "(.+?)[\?\"']/";
+    preg_match_all($pattern, $editor['text'], $matches);
+    $usedfilehashes = [];
+    foreach ($matches[1] as $matchedfilename) {
+        $matchedfilename = urldecode($matchedfilename);
+        $usedfilehashes[] = \file_storage::get_pathname_hash($context->id, 'user', 'draft', $editor['itemid'], '/',
+                                                             $matchedfilename);
+    }
+
+    // Now, compare the hashes of all draft files, and remove those which don't match used files.
+    $fs = get_file_storage();
+    $files = $fs->get_area_files($context->id, 'user', 'draft', $editor['itemid'], 'id', false);
+    foreach ($files as $file) {
+        $tmphash = $file->get_pathnamehash();
+        if (!in_array($tmphash, $usedfilehashes)) {
+            $file->delete();
+        }
+    }
+}
+
 /**
  * Saves files from a draft file area to a real one (merging the list of files).
  * Can rewrite URLs in some content at the same time if desired.
diff --git a/lib/form/editor.php b/lib/form/editor.php
index 69a78127219..d32527ab3e7 100644
--- a/lib/form/editor.php
+++ b/lib/form/editor.php
@@ -58,7 +58,7 @@ class MoodleQuickForm_editor extends HTML_QuickForm_element implements templatab
     /** @var array options provided to initalize filepicker */
     protected $_options = array('subdirs' => 0, 'maxbytes' => 0, 'maxfiles' => 0, 'changeformat' => 0,
             'areamaxbytes' => FILE_AREA_MAX_BYTES_UNLIMITED, 'context' => null, 'noclean' => 0, 'trusttext' => 0,
-            'return_types' => 15, 'enable_filemanagement' => true);
+            'return_types' => 15, 'enable_filemanagement' => true, 'removeorphaneddrafts' => false);
     // 15 is $_options['return_types'] = FILE_INTERNAL | FILE_EXTERNAL | FILE_REFERENCE | FILE_CONTROLLED_LINK.
 
     /** @var array values for editor */
diff --git a/lib/tests/filelib_test.php b/lib/tests/filelib_test.php
index 87a37bd0fe2..cb40c8fe7e8 100644
--- a/lib/tests/filelib_test.php
+++ b/lib/tests/filelib_test.php
@@ -1340,6 +1340,51 @@ EOF;
         $this->assertEquals(0, $fileinfo['foldercount']);   // No subdirectories inside the directory.
         $this->assertEquals($file->get_filesize(), $fileinfo['filesize_without_references']);
     }
+
+    /**
+     * Test confirming that draft files not referenced in the editor text are removed.
+     */
+    public function test_file_remove_editor_orphaned_files() {
+        global $USER, $CFG;
+        $this->resetAfterTest(true);
+        $this->setAdminUser();
+
+        // Create three draft files.
+        $filerecord = ['filename'  => 'file1.png'];
+        $file = self::create_draft_file($filerecord);
+        $draftitemid = $file->get_itemid();
+
+        $filerecord['itemid'] = $draftitemid;
+
+        $filerecord['filename'] = 'file2.png';
+        self::create_draft_file($filerecord);
+
+        $filerecord['filename'] = 'file 3.png';
+        self::create_draft_file($filerecord);
+
+        // Confirm the user drafts area lists 3 files.
+        $fs = get_file_storage();
+        $usercontext = context_user::instance($USER->id);
+        $draftfiles = $fs->get_area_files($usercontext->id, 'user', 'draft', $draftitemid, 'itemid', 0);
+        $this->assertCount(3, $draftfiles);
+
+        // Now, spoof some editor text content, referencing 2 of the files; one requiring name encoding, one not.
+        $editor = [
+            'itemid' => $draftitemid,
+            'text' => '
+                <img src="'.$CFG->wwwroot.'/draftfile.php/'.$usercontext->id.'/user/draft/'.$draftitemid.'/file%203.png" alt="">
+                <img src="'.$CFG->wwwroot.'/draftfile.php/'.$usercontext->id.'/user/draft/'.$draftitemid.'/file1.png" alt="">'
+        ];
+
+        // Run the remove orphaned drafts function and confirm that only the referenced files remain in the user drafts.
+        $expected = ['file1.png', 'file 3.png']; // The drafts we expect will not be removed (are referenced in the online text).
+        file_remove_editor_orphaned_files($editor);
+        $draftfiles = $fs->get_area_files($usercontext->id, 'user', 'draft', $draftitemid, 'itemid', 0);
+        $this->assertCount(2, $draftfiles);
+        foreach ($draftfiles as $file) {
+            $this->assertContains($file->get_filename(), $expected);
+        }
+    }
 }
 
 /**
diff --git a/mod/assign/submission/onlinetext/locallib.php b/mod/assign/submission/onlinetext/locallib.php
index 5ec7c6d0e08..17e342b7a13 100644
--- a/mod/assign/submission/onlinetext/locallib.php
+++ b/mod/assign/submission/onlinetext/locallib.php
@@ -169,12 +169,13 @@ class assign_submission_onlinetext extends assign_submission_plugin {
      * @return array
      */
     private function get_edit_options() {
-         $editoroptions = array(
-           'noclean' => false,
-           'maxfiles' => EDITOR_UNLIMITED_FILES,
-           'maxbytes' => $this->assignment->get_course()->maxbytes,
-           'context' => $this->assignment->get_context(),
-           'return_types' => (FILE_INTERNAL | FILE_EXTERNAL | FILE_CONTROLLED_LINK)
+        $editoroptions = array(
+            'noclean' => false,
+            'maxfiles' => EDITOR_UNLIMITED_FILES,
+            'maxbytes' => $this->assignment->get_course()->maxbytes,
+            'context' => $this->assignment->get_context(),
+            'return_types' => (FILE_INTERNAL | FILE_EXTERNAL | FILE_CONTROLLED_LINK),
+            'removeorphaneddrafts' => true // Whether or not to remove any draft files which aren't referenced in the text.
         );
         return $editoroptions;
     }