Crimestoppers is an independent charity helping law enforcement to locate criminals and help solve crimes. They have an anonymous 24/7 phone number, 0800 555 111, that anyone can call to pass on information about crime; alternatively people can send information anonymously via the Giving Information Form.
You don't have to give your name or any of your personal details. They do not trace calls or track IP addresses.
For more information visit their website Crimestoppers.