Having listened to both pieces, it sounds like the old problem of two washerwomen shouting at each other across the street from their open windows; they'll never agree, because they're arguing from different premises.
The issue is over cyclist/motorist conflicts when the cyclist is going straight ahead. The different assumptions come in when you consider whether the cyclist is "undertaking", or something else is happening. That something else is either that the cyclist is on an adjacent cycle path, or that the motorist is turning right from the opposite direction, or that the motorist overtakes the cyclist and then turns across his/her path.
Duncan Buchanan was entirely focussed on the undertaking situation. Chris Boardman was entirely focussed on the other situations. Hence, they did not agree. The only point at which their arguments even touched on each other was when Buchanan mentioned rule 72: "Do not ride on the inside of vehicles signalling or slowing down to turn left", and Boardman said something to the effect that that rule would stay, and it wasn't what he meant. Then they went back to arguing across each other.
It's unfortunate that so many people, when they hear of a side-swiped cyclist, think of undertaking. As far as I know, all the evidence is that that is the less likely scenario:
- Various statistical analyses of collections of police accident reports say that, in a collision at a junction, the motorist is two to three times more likely than the cyclist to be at fault
- Common sense says that, except in heavy traffic, the cyclist would be doing really well to manage to undertake in the first place
Boardman of course believes that a much simpler rule would keep vulnerable road users in the forefront of everyone's mind, and hence reduce incidences of the more likely scenario. Buchanan believes that it would increase the occurrence of the rarer one (though he may not realise or acknowledge that it is rarer). The job of the BBC interviewer was to recognise the problem of different premises, and bring the two onto common ground in order to get some useful debate.
Much as I usually like what Chris Boardman says, I'm not sure any of the three gentlemen got us far forward this time. Getting nowhere, in spite of lots of noise, is of course is what tends to happen when the traffic is heavy