Title text:
Other numbers are largely unaffected, but anyone using '4' for their certificate key is urged to upgrade to '5'.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3314/
Can confirm this caused a lot of confusion for the 6 months i lived in the uk as a dutch person lol. Eventually we just ended up saying the numbers.