[Neil Jones]

The C4 "Roto" was entirely computer generated - designed by Central TVs in house promotions team

Not a surprise it was computer generated, it was very similar to Central's style at the time.
Were they able to animate that to completion in house (similar to the idents) as I'm sure I read somewhere (it may not have been ITV Schools on 4 related) that this sort of work computers didn't have processing power and it had to be done in the States?

Of course if you know what you're doing these days you can knock that up to completion in an hour or so, as demonstrated here:
tvforum.uk  (although it quickly became the Ballyboy show ) - but in the 80s...