[sparky_75]

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...

The original Central brand - used from 1982 - was developed in conjunction with Minale Tattersfield - an outside design consultancy. This company was also responsible for the Thames skyline ident in the late 60s.
The Central Autumn 1985 brand (when the 'cake' ident first appeared) was developed mostly by their in house promotions and graphics department. The animation work carried out elsewhere and struck to 35mm film.

The Head of Promotions at Central - Jim Stocko was involved with the re-design of ITV Schools for the move to C4.
Not sure what computers they used for definate, but many were using some form of Commodore Amiga and Archimedes at the time. Around the same time YTV introduced their CGI Chevron - this was aparently created on Amigas - according to an article/feature run by Ace Magazine in 1987. (This work was outsourced)
I don't think Central had the equipment at the time - due to the expense - so it was likely to have been outsourced to a specialist company.
Central had been using a version of Quantel Paintbox for a little while - but not sure if those versions had the capabilities required.
By 1990 - they were using Quantel Harry and Harriet for most of their captions and graphics work - which had greater capabilities.

At some point between 1986 and 1989; Central set up The Image Facility - their Graphics Dept hiring out their services.
They would do a lot - if not all of the design work - and the Computer/Animation/Post Production work outsourced.
One of the companies used Autodesk software initially to create the wire meshes.
I'll dig out some industry magazines to see if I can find the articles.

All this would be simple and cheap these days - esp the CGI work.
I can't find it, but there was a re-creation of the C4 Schools roto on Youtube.
And quite decent job too. I think it was done in Blender.