Would I have to apply for occupation rent via the family court Ancillary Relief proceedings, or is there another legal route? (property is jointly owned, no mortgage, and stbx has excluded me from the property over past year)
There is a general rule that one co-owner can''t recover rent from another co-owner in sole occupation. The rationale being that co-owners are both equally entitled to occupation and one cannot claim rent from another (Jones v Jones  1 WLR 438, 441). There are exceptions of course, but rather than getting bogged down with the issue it''s usually better to press on with reaching a financial settlement.
If you want rent then surely your ex will want you to pay your half of the mortgage. It''s normal for these figures to "cancel out". Therefore the sole occupier of a jointly owned property pays the entire mortgage in lieu of rent. Most people consider this to be fair.