The EHIC is the replacement for the old E111 and is valid in the EEA (European Economic Union) and Switzerland.
The card, which is free to UK residents, gives access to state-provided medical treatment only, and you'll be treated on the same basis as an 'insured' person living in the country you're visiting.
The EHIC is normally valid for three to five years and covers any medical treatment that becomes necessary during a trip, because of either illness or an accident.
This might not cover all the things you'd expect to get free of charge from the NHS in the UK and you may have to make a contribution to the cost of your care.