The Department of Health has said that more than three million cards will have expired by the end of the month.
Health Minister Dawn Primarolo said: "Anyone travelling with an expired EHIC is putting themselves at risk - they will not be covered for basic medical care.
"It is vital that UK residents holidaying in Europe carry their EHIC and take out adequate travel insurance to avoid having to pay out unnecessarily for medical costs that could be covered by a valid EHIC."
The EHIC, which replaced the E111 form in 2005, entitles people to reduced costs or free state-provided healthcare in most European countries should they fall ill or have an accident.
The EHIC can be renewed online or over the phone and will be delivered within ten days; it can also be renewed up to six months in advance of expiry.
For details of the French version of the card read more about the Carte européenne d’Assurance Maladie.
Update 26/03/2010: Change to issuing of European Health Insurance Card