Never been in this situation before and its driving me mad.... Have had a crush on a guy at work now for over a year.... He's gorgeous and to me an adonis.

Never heard a woman use that word before.  That means "a very handsome young man" to those that don't know the word.

I've had a few knocks in the past and am trying to get my self esteem back up... My friends say i'm gorgeous but I have yet to believe that but know i'm not a minger....

Well you will have start believing you are gorgeous.  Even if your not it is good to have that belief, because then you have much more confidence which often leads to you being more attractive.

So I can't believe this guy would have any interest in me (Mind you people who don't know me think i'm very confident, friendly, have a laugh and have no problem speaking to people..)

If people say that, then that is the way you come across. I don't see why you have any problems with yourself.

But I become a nervous wreck near him....

People, always become nervous around people they fancy.  Research has shown that nervousness helps us look even more attractive.  So you can relax in the knowledge that you look even more attractive.  Apparently your body has a gush of adrenaline, which sends blood flow to the sexual parts of the body, for example the lips which become more red and prominent.

The signals (well my view) he looks alot, many a time I've glanced over and found him looking at me... He also does the sideways glance when we walk past (this is before I started to say Hi and he always grins and laughs and says hi now).

Very positive.

We are in the same office and we often bump into each other, smile, say hi and that's it! When I speak to people near him I can see him watching me (I have a peek at the! side) but I ignore him as I'm stupid.

Just be what you want to be, be natural.

I've even stopped dead in a corridor and turned and gone another way when he has been walking towards me

May just add to the chase for him.  But you can't keep doing that.

(How pathetic he must of thought I was stupid!)

If he thought you were stupid, he wouldn't be paying you much attention!

I've been told he's really shy too.

If, he is really shy, you need to be creating the conversational opportunities.  You don't have to have long conversations, you just have to relaxed and talk to each other like you would talk to a friend.

So, am I reading this all wrong and he's simply not interested at all and i'm being a plonker! Or am I (as I have been told) giving him the wrong message by speaking sometimes and ignoring him other times?

I don't think this is the wrong impression, because you are speaking to him sometimes and showing interest.  But what you can't continue doing is completely ignoring more times than you speak to him.  You have got to get used to talking to him. 

One way to relax yourself is to breath in through the stomach, and concentrate on breathing from the stomach.  When people are nervous they often breath from the chest and sometimes sound like they are having an asthma attack in the process. Just to re-emphasize that when you are breathing your stomach should be breathing in and breathing out, not your chest.  Practice breathing from the stomach now and before you see him, then put it into practice when you do see him.  If you are doing it right, you should find you are more relaxed, because you are breathing properly.

Just want this to stop... Shall I move office to get away from him? Or (as I've been told) try to smile and start a conversation?

Try and smile and start a conversation.  Just relax, be yourself and pretend you are talking to a friend or potential friend.