Living Wills, Final Directives, DNR, etc

So, like many around the world, my husband and I (both now in the UK) have been following the Schiavo case with some interest, and it dawned on us that we have no idea what the laws are in Britian on "advanced life support measures".  Do they have the equivilant of living wills/final directives?  What are the procedures for them?  Are they actually followed by doctors or do medical professionals have the right (like in some states) to ignore them?  How do you get them drawn up?

Thanks in advance!

Before I moved here I wrote a living will in the US.  I felt empowered and relieved to have written it.  But I have a feeling that if a US will is not valid in the UK then a living will won't be either....

any lawyers or healthcare professionals out there know this?

I believe that, with the will anyway, that if you have it filed in both countries it is recognizied in both places - but better to have a professional answer this one. 

What do I know...   

~Liza