Well I don't know whether they are dangerous or not but we bought one of these and it looks pretty good. Might fit a CO detector after reading this thread.....
Just found this thread via Google. I was looking for the same thing but then we decided to opt for a flueless gas fire to avoid having to modify the chimney. We got ours from http://www.firesgalore.co.uk/section.php/9/1/flueless-gas-fires