Thankyou, Gary. I am only middling in terms of expertise, so bear with me!
The problem I have is when I am trying to connect the keypad to the iPad, the iMac discovers it and automatically connects.
So, it seems to me, there are two steps. Somehow I need to connect the keypad successfully to the iPad. Then I need to stop the keypad being discovered (or at least connected) to the iMac.
If I took the iPad out of range and got it successfully connected, would that prevent the iMac from connecting?
Thankyou for your input.
Do both keyboards show in the iMac Bluetooth preferences ? If yes then delete both, then turn off both keyboards, then turn on only the one you want to work on the iMac thus making it discoverable by the iMac in the Bluetooth setup. Pair it and only it with the iMac. Your other keyboard when turned on should only be recognized by the iPad regardless of the proximity.