The UK will be leaving the EU/EEA without a deal, the rules for driving abroad will change after 31/12/2020.
The legal requirements of the Green Card system mean anyone driving abroad under a UK insurance policy must carry a physical Green Card.
If they intend to tow a trailer or caravan, they must also have a separate Green Card for that.
A Green Card isusually free (this may be subject to change in future) there may be an administrative charge as well and you should contact your insurer to obtainone.
We would suggest doing this at lease one month before you plan to travel.
If you travel without a Green Card, you will be breaking the law; risking a fine,seizure of your vehicle, or prosecution.
You can go to Gov.UK https://www.gov.uk/driving-abroad for further clarity on the rules and requirements.