Ms Sturgeon was incensed that Blair had ripped up a decades-long consensus on the means by which Scotland could legitimately express a desire to become independent, but Dewar stood his ground - he pointed out that it was possible/likely that if the SNP ever won a majority of seats, they would do so on a minority of the vote, and that couldn't possibly be a mandate for independence.
Essentially Dewar was making a lot of the points Ms Sturgeon now makes about the nature of a 'legitimate' indy mandate, and yet Ms Sturgeon emphatically rejected them at the time and branded them a democratic outrage. She was adamant that the truly legitimate path to independence was one that didn't even involve a referendum at all.
Given the circumstances, that might be a rather useful piece of footage to have, although it would be like looking for a needle in a haystack. The only people who may have a realistic chance of tracking it down would be BBC employees with access to 'BBC Redux' - a sort of on-demand digital archive of all BBC programmes going back many years.