I am using Firefox and when I try to connect using mycompany.quickfile.co.uk everything is OK.
But when my accountant tried to connect using www.mycompany.quickfile.co.uk it failed with an “Insecure Connection” with the message "Your connection is not secure
The owner of www.mycompany.quickfile.co.uk has configured their web site improperly. To protect your information from being stolen, Firefox has not connected to this web site.
Report errors like this to help Mozilla identify and block malicious sites"
This worried my accountant and he thought that your website must have been hacked, rather than just misconfigured!