How do I forcibly unpair my Magic Keyboard from my Mac, so that I can pair it with my iPad?

Fixed, I had to remove the wired USB keyboard i had plugged in, and I also held the power button down on the magic keyboard while bluetooth searching for it.

The response on this forum dated Dec 24, 2010 2:29 PM helped me: https://discussions.apple.com/thread/2693201?start=0

No - the pairing record on the Mac will remain until you remove it from that Mac. It's a sleeping dog situation when the Mac isn't nearby.

You can get a factory wipe of Apple's Bluetooth keyboards using this debug feature in macOS: - https://apple.stackexchange.com/a/15291/5472

• Hold shift and option (only) when clicking on the Bluetooth icon in the menu bar of the Mac
• Select Factory Reset for each device you wish to reset