Captcha Not Working - Can stil send form when it is empty

Hi, I've just added recaptcha to avectura.co.uk (on the home page on the right). I tested the form and all seemed to be going well. Then I performed a test with the recaptcha field empty and it still worked? Any ideas why. -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.