Here's the response from Canon:
Thank you for contacting Canon product support. We value you as a
Canon customer and appreciate the opportunity to assist you. I am
sorry that your PIXMA MP560 is not recognizing the CLI-221 and PGI-220
ink tanks you purchased.
The reason that the printer is not recognizing these ink tanks is
because these were purchased here in the United States and your PIXMA
MP560 was from the United Kingdom. The ink must be purchased from the
Canon division where you purchased the printer. Unfortunately, this
means that the ink from the United States would not work in your UK
PIXMA MP560. It would need to come from a United Kingdom dealer.
I am sorry for any inconvenience this causes. Please let us know if
we can be of further assistance with your PIXMA MP560.
TLDR Canon region locks its print cartridges.
Update: It is possible to alter the region of cartridges, notably using a "redsetter" device, which also resets ink levels (as electronically recorded).