With the Prestel “standard” becoming popular, with the increasing number of dedicated terminals or software terminals available, and the ease of use for a non-technical audience, many companies started using it for their in-house systems. BT promoted their “Private Prestel” service, whereby you could rent space and users on the Prestel computers which would be kept entirely separate from the public side, and many other companies popped up offering software and hardware solutions for running entirely in-house.
As with Prestel itself, anything you think of that can be done on the Internet, or “Intranet”, could be done through viewdata. Corporations used them to disseminate price lists and news, handle email and take orders, and pretty much anything they fancied. All in a nice user-friendly format.
Personally, I had experience of the Ferranti system – I was only an apprentice at the time, but we had terminals in the training centre that could dial up the corporate system using the internal telephone network. Saldly, my only memories of this are using the editing facilities to produce, or reproduce, some nice pictures.