I have had horses that you can't catch for anything. And by the time I have had them a month or two, almost all can be caught at any time.
I have found that food is one of the best ways to catch them. They come to me, and they get their food. If they don't, I feed it to someone else or take it back to the barn. (bucket training) No chasing. I gave up the chasing bit as it only worked for me when in a smaller area. If in a large 2 acre field, forget it as they know that I physically can't get to them to make them run.
What works the best for me is to do simple catch and release routines. Similar to what Jayne said. I ALWAYS give a treat for being caught on those that are hard to catch. What I do is catch the horse, feed it it's grain, and then immediately release the horse. I do this for a while. Sometimes I feed it in the pasture, other times I take them out and just brush them while they are eating the grain and then put them back. No working them at first and then later on do it randomly.
You see, most likely your horse has learned that being caught means always being worked. If you catch the horse, he will have to do something. He is a very smart animal and really doesn't want to be worked. He has learned that people won't go through all that effort just to catch him and then NOT work him. So you will have to play games and do catch and release more often to help with that.
I also have taught all of my horses to eat those hard starburst peppermint candies. The reasons I do so are many, but I find that once they learn that it tastes really good, and that the wrapper making noise means they are about to get a treat, they will do just about anything at the noise of the wrapper. Plus I can carry these in my pocket for an immediate reward.
Now with all of that said and all of the good ideas posted in the other replies, I have one more suggestion.
I had the pleasure of working with a "nervous" type of horse. He was never abused and we had him from the time he was a weanling. Koin was perfectly fine once he was caught, but a real pill to catch. Running this Arab didn't work as he would just get more difficult to catch if we did that. He didn't associate the pressure on pressure off thing the way that most horses did. He just knew that we were going to work his fanny off if we showed up in the pasture he was in. And food didn't always work well either. But we finally got into his head and figured it out.
You see, he was seeing us as a preditor and he was prey. Remember, we have eyes in front of our head and this makes us preditors in a prey animal's eyes. (Funny, but kids had no problem catching this horse! Maybe Koin understood that kids are not dangerous preditors!) Anyway, what we learned was that we would look the horse in the face and square off to him and then deliberately try to walk right up to him. Now he acted on the flight instinct and of course we would chase. Hummm. Sounds like a preditor prey situation happening.
So what we did was change our approach to him. First, we only looked at his feet. Like your horse, we knew he wasn't going to endanger us, so we gave him that trust. By looking down, you are not focussing on him and not making him feel that preditory pressure. Next, we didn't walk straight up to him by facing him and squaring off to him. What we did was align our bodies so that we were facing the opposite direction he was. In other words, our left side was next to his left side so we were parallel to him in "head to tail" fashion. Again, this removed the preditory pressure from him as our body was no longer a threat to him. Now we then kind of just sidepassed over to him. This way we kind of approached at an angle with no preditory pressure.
We found that any adult could catch this horse in this fashion, halter in hand or not, and was the only thing that worked 100% of the time. I have since learned that many horses respond to this approach instead of running them. Of course I do spend the extra time with these types of individuals to do lots of catch and release work. Sometimes they get a treat, other times they just get the halter put on, petted, and they turned loose. For me, the catch and release routines are a very important part of training on the hard to catch individual.
Of course nothing may cure him. You just may have to accept that he is the way he is. And sometimes just accepting that makes a difference as well. Koin was one that we learned to accept that he would never be an easy to catch horse using a "direct aproach". We learned to accept him as he was and "slide" up to him. After many years of owning him, we found a way to meet middle ground with him.
Keep trying, and don't give up on him.