A source for having the right of way meaning that you shouldn't exercise caution?

I don't care what the right of way rules in the UK are, I'm taking exception to your argument that exercising caution implies lacking a right of way, suggesting that having the right of way means you don't have to exercise caution. The right of way is only relevant if you survive to hash things out in court, it won't bring you back from the dead. Even if you have the right of way, you'd be suicidally stupid to not still exercise caution, particularly when doing something usual and obviously dangerous.