Yes, you can claim passing off even if you don't have a registered trademark. Passing off is a common law tort that protects unregistered trademarks and other forms of intellectual property. To succeed in a passing off claim, you must prove that you have built up a reputation or goodwill in your business or product, that the defendant has misrepresented their goods or services in a way that is likely to cause confusion or deception among consumers, and that you have suffered damage as a result.