From 28 September, if you wish to drive in the EU you will need to show a UK sticker or number plate sign that has the Union Flag (Union Jack).
This has not been widely publicised. However, you could fall foul of an overzealous border guard and be turned away if your vehicle doesn't carry the right insignia. More detail can be found on the UK Government website.
The UK Government page states:
“On or after 28 September 2021 You will need to display a UK sticker clearly on the rear of your vehicle if your number plate has any of the following:
- A GB identifier with the Union flag (also known as the Union Jack)
- A Euro symbol
- A national flag of England, Scotland or Wales
- Numbers and letters only - no flag or identifier
If your number plate includes the UK identifier with the Union flag (also known as the Union Jack), you do not need a UK sticker.
If you’re in Spain, Cyprus or Malta, you must display a UK sticker no matter what is on your number plate. If you have a GB sticker, cover or remove it.”