Sorry Barry,
I think you desire to spin any Cameron/Tory action into a positive has taken a leap to far here. the interview can be heard at
http://www.bbc.co.uk/iplayer/console/b010vy93 - set the timer to 2 hrs 10 minutes to get the crucial bit of the programme. Cameron was evasive, refusing to condemn the no campaign inflammatory claim that AV would result in the deaths of babies and under equipped troops in Afghanistan and came across as someone primed to bolster his own policies as "robust" and to try and deflect attention away from his own gaps by using the "lead broadcaster" comment in a disparaging way.
John Humphries has been better but it is clear that Cameron has had his media training and knows how to stonewall.
I would think it's just not interesting or engaging to the average member of the electorate and will have a negative affect on turnout; that would suit Cameron and his cronies so perhaps it was intentional on his part.