Thanks for the reply.
I have tried that command in the config file but it didn't make any difference. I'll give it another go in case I made a mistake.
If I boot my RPI it will turn the TV (Samsung) on.
The reason I want to turn CEC off is that the RPI is connected to my AV amp and when I turn that on with the RPI active it will switch to the RPI output regardless of what else is running through the amp.
It's no major problem just thought if there was an easy way of turning it off CEC I'd give it ago.