My comments on the video where in no way blaming you for the undertake, I was highlighting the danger of not checking behind and no signal before you turned, regarding riding in the middle of the road I would rather pull up at the kerb and let vans etc. get past instead of getting into a no win duel with one of them.
John, Kev has already said that he did indeed signal prior to the turn (and I'm assuming did an over the shoulder check too?), it's just that it happened before the film clip starts. I take your point that ideally you should signal again for the actual turn but I believe the point is rendered moot in this case given that he had already signalled to the vehicle that, very audibly, remained behind him up until that point that he was turning right.
If we're being honest, none of us signal as we turn, it would be incrediby dangerous. We all have to signal before we turn. It then becomes an issue of how long before you make the turn is it acceptable to have signalled? It's down to common sense, speeds, conditions, etc. There is no rule here although you would think the earlier the better and the longer you signal the better, but then is it really given that you're riding ability (steering, braking, stability) is compromised while signalling? Like I say, there is no rule.
Really, the merits of signalling timing and length pale in to insignificance given that a van driver, in his anger, deliberately almost knocked a cyclist off his bike in to the path of oncoming traffic. I would go as far as to say that signalling is not even relevant here. This undertaking is so dangerous and so deliberate that no matter what the signalling prior to it, it can't be excused. If I had just signalled left, then right, then up, then down, I still have the right for someone not to deliberately try a move that stands a good chance of killing me even though they are now thoroughly confused as to what my intentions are.
By the way, I'm riding without a mirror at the moment and I regularly do exactly what you suggest on a right turn off a busy road on my morning commute if there is no break in traffic behind me. I slow down at the kerb and wait for a break before continuing. It's the only foolproof way really and even though some cyclists would say it is unneccessary I am fully with you on this one. That said, even when there is a break and I'm in the middle of the road signalling, I have still had people floor it and overtake me just as I would be turning.
It's sad to say that I am gradually coming to agreement with others on this forum that the only way to keep cyclists and drivers safe on our congested narrow roads is to separate the two completely.
Again, I find myself saying to another member of the forum that I'm glad they didn't get seriously injured or killed. Every time I say it I worry more and more about the future of commuter cycling in this country. I find myself offroad on my MTB more and more these days but there simply isn't an offroad route to most people's work, myself included.