Well, good news today. My farrier came out rather unexpected today and said he wanted to deal with the problem. Freddies hooves had gotten very long, and we decided to try giving them a aggressive cutting back, which would leave him lame for a couple days, but should help him balance more on his toes, and thus alleviate his pain.

There was a chance with the cut that we could injure him further and he would be lame for life. But seeing as he always seemed to be I agreed to it.

Freddy did incredible well with the cut, he was a bit sensitive, but is sound and happy. When we cut them back we found a deep rooted absess in his hoof!

This could be the reason for his unsoundness and it may not be navicula.
The absess has been around for a while, and was very deep in the hoof, but my farrier managed to find the pocket, and burst it, once it's drained it can heal and then he should be alright.
This doesn't mean he doesn't still have navicula, but it's becoming alot less likely. :)