Pete Frame, whose hand-drawn genealogical trees map the fraughtly entertaining internal relationships of rock's institutions, has explained how this second series attempts to capitalise on the strengths of the first: "Because it's a peak-time show, the producer, Francis Hanly, and I went for people who were going to be as funny and eloquent as possible," he says. "We've tried not to make things too trainspotterish."
Though first and foremost a thoroughly researched documentary series, Rock Family Trees' judicious use of wry, anecdotal footage is one of its strengths. The programme highlights both the incestuousness and the ridiculousness of rock but with affection. It's a gentle reminder that most bands have had their Spinal Tap moments.
In "The Prog Rock Years", which centres around the careers of Yes and ELP, keyboard wizard Rick Wakeman recalls a late-Sixties gig with The Strawbs where the bands shared a bill with circus performers: "What you did was you accompanied the various acts," he remembers. "They had Arthur Brown playing for the trapeze artist and we, The Strawbs, were playing for the child jugglers. Suddenly there was a bit of a cheer from the crowd and this old boy with a handlebar moustache jumped up on stage and started waving a stick around. I thought: `Who's this old git?' and pushed him off. The police arrested me. How was I to know it was Salvador Dali?"
With accessible, fastidiously-edited portraits of the early Sixties Merseybeat scene, the Manchester club scene which had New Order at its epicentre, and the late Sixties folk movement that spawned The Mamas and The Papas in the States, the scope of the new series is impressive. John Peel's relaxed narration links choice archive footage with interviews, while Frame's drawings - often accompanied by an appropriate montage of album artwork and memorabilia - provide ideal pit-stops for cross-referencing and plot denouements.
Older, wiser, and just that little bit less precious, most artists portrayed here can laugh at themselves. Billy J Kramer, though, interviewed for The Mersey Sound episode, seems less able to let go of old rivalries. Obviously keen to challenge the view that his own band, The Dakotas, were simply Beatles wannabees, Kramer remembers Brian Epstein giving him the original demo tape of John Lennon's "Do You Want To Know A Secret", a song with which he and The Dakotas would later score a hit. Kramer goes on to say that at the end of the demo, Lennon "sort of apologised for the quality of the song and flushed the toilet". The inference is clear.
With around 250 bands regularly gigging in and around Liverpool at the time, demand for strong original material was high. Even one of the Fab Four's finest, though, was deemed unworthy of Kramer.
"Different writers have said that Paul McCartney never offered `Yesterday' to anyone," says Kramer; "but when I was doing a summer season in Blackpool, he played it to me. I said, `I don't like it Paul. It's boring and I want a rock 'n' roll song.'"
If Kramer seems a tad prickly, then in contrast, the former Adam and The Ants guitarist, Marco Pirroni, is refreshingly frank about how Adam's image influenced the Ants' writing. "`He's a pirate on land and he wears a good hat' - that was the sort of thing," he explains in "Banshees and Other Creatures". With indisputable logic, Pirroni adds: "When you've got a song about a highwayman, it has to be called `Stand And Deliver', and it has to go `dum, diddle-lum, diddle-lum'." Adam himself, alias Stuart Goddard, is less willing to trivialise his back catalogue. This tactic of allowing sidemen to have a good giggle at the expense of their more celebrated former leaders is one which Rock Family Trees has used effectively time and again.
Cleverer still, is the way that the programme's interviewers can gently cajole musicians into talking utter nonsense with no attendant sense of irony. And when heavy metal comes under the spotlight in "Sabbath Bloody Sabbath", we're not short of examples. Witness singer Ronnie James Dio on one of the bands he was in before Rainbow and Black Sabbath: "We just became Elf, which made sense, because we were all really small men. My cousin was barely five feet tall, and I'm like five four-and-a-half, five- five. We would come out on-stage and the audience wouldn't know what to make of these little tiny people. Then we just bludgeoned people to death with our level of power."
Like the programme on Merseybeat, tonight's snapshot of the late Sixties folk scene in Greenwich Village has value as a social history, but ultimately "California Dreamin'" is probably the least engaging episode of this series. The Americans' reluctance to dish the dirt makes for rather safe viewing, and given the quality of the rest of the series, it's an odd place to start.
To paraphrase Mick and Keef, though, Rock Family Trees is one of the few examples of the pop documentary genre to declare: "It's only rock 'n' roll, but we like it."
Any artists approached to appear in a third series should be aware that the more self-effacing they are, the better they will come across.