(as) artful as a wagonload of monkeys
Impish or mischievous. ("Cartload" can be used instead of "wagonload.") Primarily heard in UK. Don't let those boys sit together—they're as artful as a wagonload of monkeys.
(as) clever as a wagonload of monkeys
Impish or mischievous. ("Cartload" can be used instead of "wagonload.") Primarily heard in UK. Don't let those boys sit together—they're as clever as a wagonload of monkeys.
as artful (or clever) as a wagonload (or cartload) of monkeys
extremely clever or mischievous. British informal