Compared to American comics, crossovers in British adventure comics are fairly rare. Of course the strips in TV21 inhabited a shared universe, as do several of the strips in 2000AD, but it was very uncommon for a strip in one comic to link to a different strip in another title, especially in the 1960s.
However in the mid-sixties, Smash! and Terrific did just that. Obviously the Marvel reprints they used were doing it all the time, but two of their originated British strips also had a connection.In Smash! No.36 (dated 6th October 1966) the evil Doctor Fear apparently met his demise in the Rubberman strip (art by Alfredo Marculeta). "This time there was no doubt." a caption told us, "Doctor Fear would never again bring terror to mankind."
Surprisingly a year later in Terrific No.25 (dated 30th Sept. 1967) who should turn up in the Appointment With Fear series than - Doctor Fear! With a flashback sequence to that Rubberman strip and an explanation as to how he survived...
But there was another twist. A few weeks later in Terrific No.28, it was revealed that it was only someone impersonating Doctor Fear in an elaborate ruse to test the story's hero, Don Starr! "I'm sorry about the Doctor Fear act - but I had to be certain you didn't scare easily!" says Jermyn Forster. Then Don Starr has his head turned by the imposter's pretty secretary and he's off on another adventure.
As much as I like those comics I have to admit that this was an example of British comics at their silliest. Was the revelation of Forster as an impostor planned from the outset or did the scriptwriter just make it up as he went along week by week? Who knows? But at least it ticked the boxes to be an exciting serial and the artwork was suitably dramatic.