If the UK leaves without a deal, UK citizens driving their vehicle within the EU would be required to obtain and carry a physical Green Card in order for your UK car insurance to be applicable in the EU. These cards would be issued by insurers and you may be charged a small fee to cover administration costs.
Speak with your insurer for more information on obtaining a Green Card for any trip on or after 29 March 2019.
The ABI – the trade body for the insurance industry – recommends you contact your car insurance company at least one month in advance of travelling.
For more information please visit - https://www.gov.uk/guidance/uk-nationals-travelling-to-eu-essential-information.