Check the date on your computer. If it's wrong it could cause problems with recognising valid security certificates.
Otherwise, if you're 100% sure that the web address is what you'd expect it to be, click 'Proceed anyway':
http://www.google.com...py?hl=en&answer=98884
The relevant web address should start with 'https' and end with 'williamhill.com'. If it's anything else (such as 'william-hill.com' or 'williamhill.com.something.com') you're being directed to a false page).
Or, better still, fllow the advice you've bben given and use Firefox!
Chris