UK-registered cars will need to display a GB sticker any EU country after Brexit, the government has said.
New government advice said the sticker must be displayed in any EU country.
Motorists from the UK driving are currently advised to display the sticker, but the rule is not widely enforced.
The advice was issued on the Get Ready site, which is accompanied by a major advertising campaign, launched on Sunday and unequivocally states that Brexit will happen by the end of next month. It asks users a series of multiple-choice questions and spells out the precautions that individuals should take immediately to make sure they are prepared for the UK to crash out of the EU without a deal.
The advice applies to cars registered in all parts of the UK, including Northern Ireland.
The sticker, a white oval containing the letters GB, standing for Great Britain, must be displayed at the rear of the vehicle.
Northern Ireland is not a part of Great Britain – which is made up of England, Scotland and Wales – but the GB sticker is used for cars from all parts of the UK.
The rule will apply to drivers even if their number plate includes a GB logo.
British citizens resident in the UK are also warned to ensure that their passport has at least six months to run and told they may once again have to pay roaming charges on their mobile phones.
