The first thing you need to know is the number to call in an emergency in the UK. The number is 999 not 911. When you call the number you will be asked first of all which service you require, then they will trace your call and repeat the number out loud, then they will ask you what you want all of which takes only a few seconds but can seem like an eternity.
Health care is free to all European Union residents as well as common wealth residents. If you are not a resident in one of these countries make sure you have adequate health insurance or you could be left facing a very large bill if you are unfortunate enough to get into an accident whilst in the United Kingdom.