I could not find any graphical method so I had to do it this way:
First ALWAYS backup configuration files ! !
once backed up edit main.conf file
sudo cp /etc/bluetooth/main.conf /etc/bluetooth/main.conf.OLD
Inside main.conf look for entry:
sudo nano /etc/bluetooth/main.conf
and change the value to false
InitiallyPowered = true
Save with Ctrl+X and restart GDM to see the effect :
Remember to save any file in use before restarting the graphical session
I have read this tutorial but seems a little bit out of date.