Was patting a lovely TB today, he was loving me patting his nose, then he started to raise his head and then he showed me his teeth, so i walked off, was this a sign he was going to bite me??
Sounds like he was.
Did he curl his top lir up over his nostrils? If so, he was only trying to get a better smell of you/something strange. Horses aren't like dogs, they don't bare their teeth before biting. Watch the ears - much bigger clue of mood
Was it like this?
http://www.northernequine.com/images/Flehmen.jpg
http://content.answers.com/main/content/wp/en/5/56/Mareflehman.jpg
In which case he was scenting you.
I think its most likely he was just trying to sniff you out but its hard to know from a verbal description. But also bear in mind it might have been a sign of affection. My pony sucks and nibbles on my arm a lot, sometimes he nips a bit hard but I know he doesn't mean to hurt me. I usually just step back from him so he knows it was too hard. I'm sure his behaviour is a sign of affection as he usually does it after I've been playing with him or we've had a particularly enjoyable ride (for him as well as me). You said the horse seemed to be enjoying being petted so maybe he just wanted to show you he liked you. However, I think you did the right thing to walk away. You don't know this horse and its better to be safe than sorry, especially as you seem a little nervous (sorry if i've misread that) and a bite would probably put you off a lot.
No he showed his top and bottom set of teeth.