Panic over...
Thank you, this worked first time. Had to force shut down with power button, waited 15 seconds then turned on again, held fn+eject on wireless keyboard straight away and disc ejected a few seconds later - iMac (27-inch, Late 2009).
shut computer down, while holding the eject button on the wireless keyboard, turn computer on, eject as designed!!!
Thank you, this worked first time. Had to force shut down with power button, waited 15 seconds then turned on again, held fn+eject on wireless keyboard straight away and disc ejected a few seconds later - iMac (27-inch, Late 2009).