I'm the King of Scotland and I control 100% of the British Isles. I'm a Lollard, and I used the Holy War CB to take control of the islands from the hands of the Catholics and the Norse. However, I can't declare a holy war against France just across the water.
Normally you can declare a holy war against someone with adjacent territory or across up to 2 sea zones. So, France should be in range, since we're touching the same sea zone. Is this a bug, or intentional?