Oddly in the US this printer does not ship with a tray to print on CD or DVD printable media, but you can purchase a tray separately and enable the feature. I haven't been able to confirm this but it appears that it was disabled in this country because someone other than Canon holds a patent on that feature (which sounds silly to me... like holding a patent on printing on paper) and they would not license it to Canon.
You'll also have to remove the plastic door that was placed over the CD/DVD tray insert slot. Just open the printer, and snap it off by pulling or prying. This was easier than I expected and took only a few seconds. I only pulled it off with my hand (and fingernails.) No tools required.
Anyway, to switch it to UK (instead of US) mode and enable printing, follow these instructions:
1. Plug the printer in, but leave it powered off. If it is already on, turn it off.
2. Press and hold the Stop/Reset button.
3. While still holding the Stop/Reset button, press and hold the Power button.
4. Hold both of them down for 5 seconds, then release the Stop/Reset button, continuing to hold down the power button.
5. Press and release the Stop/Reset button 2 times.
6. Release the power button.
At this point the printer should power on, but it will enter a special service mode.
7. Wait until the green copy light on the control panel stops flashing. This takes about 30 seconds.
8. (Optional) If you wish, you can press the Stop/Reset button 1 time, then press the Power button, and a ROM page will print. It should indicate US region at the top.
9. Press the Stop/Reset button 5 times to enter the "Set Region Mode". Then press the Power button.
10. Press the Stop/Reset button 4 times for Europe/UK (3 times for the US if you wish to change it back later). Then press the Power button.
11. (Optional) If you wish, you can press the Stop/Reset button 1 time, then press the Power button, and a ROM page will print. It should indicate Euro region at the top.
12. Press the Power button 2 times to save the changes.
I purchased my CD/DVD tray Type D from here: annocjr on eBay