For info, the web addresses www.rizla.com and www.rizla.co.uk (assume that you tested both) appear to be protected via a secure Internet Proxy Service provided by a web company named Incapsula (www.incapsula.com).
If of interest, you can find this information out by initially performing an on-line Name Server lookup to determine the actual Internet address (IP number) of rizla.com or rizla.co.uk
e.g. goto
http://www.kloth.net/services/nslookup.php then in the 'Domain' window enter rizla.com (or rizla.co.uk).
Note the IP address number returned (149.126.74.106) then in your Browser address bar enter that IP address. It will respond with a 'Proxy failed to resolve name' message and on that page you will see the provider as 'Incapsula'
Not sure, but it is possible that the ISP internet domain that you are using has been banned at some previous point from access to the Incapsula / Rizla web services e.g.due to recent or previous Network Denial of Services attacks emminating from your ISP network domain provider etc, or it could be just be an incorrect security check error on their part!
If that is the case there may be a denial timeout period running which may 'release' a ban at some point in the near future, but more likely to be on a permanent banned list!.
Alternatively you could try ringing, I believe the rizla.co.uk telephone number is 0115 924 2888.