diff --git a/docs/en/02_Developer_Guides/09_Security/00_Member.md b/docs/en/02_Developer_Guides/09_Security/00_Member.md
index 41d801e96..6bca454c9 100644
--- a/docs/en/02_Developer_Guides/09_Security/00_Member.md
+++ b/docs/en/02_Developer_Guides/09_Security/00_Member.md
@@ -134,6 +134,39 @@ will be created and associated with the device used during authentication. When
 for all devices will be revoked, unless `[api:RememberLoginHash::$logout_across_devices] is set to false. For extra security,
 single tokens can be enforced by setting `[api:RememberLoginHash::$force_single_token] to true.
 
+## Acting as another user ##
+
+Occasionally, it may be necessary not only to check permissions of a particular member, but also to
+temporarily assume the identity of another user for certain tasks. E.g. when running a CLI task,
+it may be necessary to log in as an administrator to perform write operations.
+
+You can use `Member::actAs()` method, which takes a member or member id to act as, and a callback
+within which the current user will be assigned the given member. After this method returns
+the current state will be restored to whichever current user (if any) was logged in.
+
+If you pass in null as a first argument, you can also mock being logged out, without modifying
+the current user.
+
+Note: Take care not to invoke this method to perform any operation the current user should not
+reasonably be expected to be allowed to do.
+
+E.g.
+
+
+    :::php
+    class CleanRecordsTask extends BuildTask
+    {
+        public function run($request)
+        {
+            if (!Director::is_cli()) {
+                throw new BadMethodCallException('This task only runs on CLI');
+            }
+            $admin = Security::findAnAdministrator();
+            Member::actAs($admin, function() {
+                DataRecord::get()->filter('Dirty', true)->removeAll();
+            });
+        }
+
 
 ## API Documentation
 
diff --git a/src/Assets/AssetControlExtension.php b/src/Assets/AssetControlExtension.php
index cda497a82..4a6d9f731 100644
--- a/src/Assets/AssetControlExtension.php
+++ b/src/Assets/AssetControlExtension.php
@@ -111,9 +111,11 @@ class AssetControlExtension extends DataExtension
         }
 
         // Check if canView permits anonymous viewers
-        return $record->canView(Member::create())
-            ? AssetManipulationList::STATE_PUBLIC
-            : AssetManipulationList::STATE_PROTECTED;
+        return Member::actAs(null, function () use ($record) {
+            return $record->canView()
+                ? AssetManipulationList::STATE_PUBLIC
+                : AssetManipulationList::STATE_PROTECTED;
+        });
     }
 
     /**
diff --git a/src/Security/Member.php b/src/Security/Member.php
index 129adb8e9..77f8c0d9c 100644
--- a/src/Security/Member.php
+++ b/src/Security/Member.php
@@ -871,6 +871,40 @@ class Member extends DataObject implements TemplateGlobalProvider
         }
     }
 
+    /**
+     * Allow override of the current user ID
+     *
+     * @var int|null Set to null to fallback to session, or an explicit ID
+     */
+    protected static $overrideID = null;
+
+    /**
+     * Temporarily act as the specified user, limited to a $callback, but
+     * without logging in as that user.
+     *
+     * E.g.
+     * <code>
+     * Member::logInAs(Security::findAnAdministrator(), function() {
+     *     $record->write();
+     * });
+     * </code>
+     *
+     * @param Member|null|int $member Member or member ID to log in as.
+     * Set to null or 0 to act as a logged out user.
+     * @param $callback
+     */
+    public static function actAs($member, $callback)
+    {
+        $id = ($member instanceof Member ? $member->ID : $member) ?: 0;
+        $previousID = static::$overrideID;
+        static::$overrideID = $id;
+        try {
+            return $callback();
+        } finally {
+            static::$overrideID = $previousID;
+        }
+    }
+
     /**
      * Get the ID of the current logged in user
      *
@@ -878,6 +912,10 @@ class Member extends DataObject implements TemplateGlobalProvider
      */
     public static function currentUserID()
     {
+        if (isset(static::$overrideID)) {
+            return static::$overrideID;
+        }
+
         $id = Session::get("loggedInAs");
         if (!$id && !self::$_already_tried_to_auto_log_in) {
             self::autoLogin();
@@ -886,6 +924,7 @@ class Member extends DataObject implements TemplateGlobalProvider
 
         return is_numeric($id) ? $id : 0;
     }
+
     private static $_already_tried_to_auto_log_in = false;
 
 
diff --git a/tests/php/Security/MemberTest.php b/tests/php/Security/MemberTest.php
index f68573bd1..12b0a8b96 100644
--- a/tests/php/Security/MemberTest.php
+++ b/tests/php/Security/MemberTest.php
@@ -1402,4 +1402,66 @@ class MemberTest extends FunctionalTest
         $userFromSession = Member::currentUser();
         $this->assertEquals($adminMember->ID, $userFromSession->ID);
     }
+
+    /**
+     * @covers \SilverStripe\Security\Member::actAs()
+     */
+    public function testActAsUserPermissions()
+    {
+        $this->assertNull(Member::currentUser());
+
+        /** @var Member $adminMember */
+        $adminMember = $this->objFromFixture(Member::class, 'admin');
+
+        // Check acting as admin when not logged in
+        $checkAdmin = Member::actAs($adminMember, function () {
+            return Permission::check('ADMIN');
+        });
+        $this->assertTrue($checkAdmin);
+
+        // Check nesting
+        $checkAdmin = Member::actAs($adminMember, function () {
+            return Member::actAs(null, function () {
+                return Permission::check('ADMIN');
+            });
+        });
+        $this->assertFalse($checkAdmin);
+
+        // Check logging in as non-admin user
+        $this->logInWithPermission('TEST_PERMISSION');
+
+        $hasPerm = Member::actAs(null, function () {
+            return Permission::check('TEST_PERMISSION');
+        });
+        $this->assertFalse($hasPerm);
+
+        // Check permissions can be promoted
+        $checkAdmin = Member::actAs($adminMember, function () {
+            return Permission::check('ADMIN');
+        });
+        $this->assertTrue($checkAdmin);
+    }
+
+    /**
+     * @covers \SilverStripe\Security\Member::actAs()
+     */
+    public function testActAsUser()
+    {
+        $this->assertNull(Member::currentUser());
+
+        /** @var Member $adminMember */
+        $adminMember = $this->objFromFixture(Member::class, 'admin');
+        $memberID = Member::actAs($adminMember, function () {
+            return Member::currentUserID();
+        });
+        $this->assertEquals($adminMember->ID, $memberID);
+
+        // Check nesting
+        $memberID = Member::actAs($adminMember, function () {
+            return Member::actAs(null, function () {
+                return Member::currentUserID();
+            });
+        });
+        $this->assertEmpty($memberID);
+    }
 }