The YouTube links can still be found here. I hope that they may be useful.
I would be interested to get any comments on this material. To me, it does little to support the idea that there is a single identifiable accent that could be called RP, even if you divide the speakers into different sub-groups and label their accents "Conservative RP", "Mainstream RP", "Advanced RP", "Juvenile RP", "Luvvie RP" or whatever.