Ooh, that was interesting, thank you... It has brought me to the Linesman Mediator system.... lots of reading and learning to do on this topic too!
I will try and get in touch with him, thanks for the pointer.
There is one interesting line on Wikipedia:
https://en.wikipedia.org/wiki/Linesman/Mediator stating: "The interception side was only ever used in the training role of the School of Fighter Control." Difficult to avoid speculating, but some conclusions could be guessed at here regarding the role of Lightnings equipped for Data Link.
Cheers, Scott