IanH wrote:
Then tug him!

Classic!
Crosthwaite is indeed a great example, with two such junctions 40 yards apart!
Ultimately, I suppose its just one of those great road design "imponderables" that keep us on our toes and make driving such a process of continual analysis and learning, but here are a couple more thoughts...
Mention was made of using road position to make our intention clear to the other road user. My humble suggestion here (and something I try do to) is not to move to the right on approach, but to do something slightly more subtle. Move to the left for a conventional approach to the RH bend, but instead of the normal "late apex" to maximise vision do the exact opposite. Start the turn early and gently, such that you start to sweep across the other drivers path much earlier than you would otherwise do. This hopefully makes your intention clear whilst you are still a good distance away from the other vehicle, and also gives you more time to do something about it should he then ignore the G/W.
Incidentally, in my original example I was assuming that the other user was already at the G/W line, so the dilemma was concerned with whether he would decide by your lack of indication that you intended to go straight on, rather than follow the road across his path. I hadn't considered the possibility Ian raised, of the other car still approaching the junction, in which circumstance I can only nod vigorously in agreement at his advice to manage speed / timing to remove the conflict altogether.
The final point is a bit more subtle still, and concerns something Paul has touched on in the past, ie the distinction between things that affect us as individuals, and things that affect drivers as a "system". This may be a bit tenuous, but imagine the other driver is a bit dim, and is in some doubt about whether I should indicate to show that I intend to stay on the main road. In this specific circumstance, if I do indicate then it will assure my safety by confirming my intention in the mind of the other driver (even though there should not have been any ambiguity in the first place). That deals with the particular instance from the perspective of the individual, but from the perspective of the system I am giving a bad message, as I am strengthening the belief in the other drivers mind that vehicles turning right will indicate. So when tomorrow he arrives at the same junction he pulls out slap in front of someone else because they didn't give the (unnecessary) indication.
What a great paradox! In the single instance my action reduces ambiguity, yet at a system level it increases it!