Hasn’t there literally just been a landmark case with this, whereby a Canoer was charged £10k for his actions. It was said to be definitive that you can’t just paddle where you fancy.
The trouble with this lot is, unlike us, they wish for unfettered and unchallengable access and wish to get that as a right rather than a contract. We pay a licence fee and must have the land owners permission, all pretty logical.
There may be some loose corner to pick at but it’s pretty simple, no you may not just wander through people’s land irrespective of the mode of transport, unless there’s a right of way such as a public footpath or navigable route. A non navigable river with no history as one, is not a navigation route or a right of way. It’s called trespass, it’s really rather simple, despite the nonsense it’s rolled in.