There's a couple of notable firsts herein: The DOCTOR WHO special is not only the first (of many) spin-offs from the weekly/ monthly/ magazine but also the first (of many) reprints of The Iron Legion, the first adventure from the 1979-launched weekly.
CAPTAIN BRITAIN was the first UK solo-outing for the nation's champion since his own weekly was unceremoniously axed back in '77 and, arguably, the beginning (along with his appearances in HULK COMICS' Black Knight strip) of his long road back.
WESTERN GUNFIGHTERS was part of a run of specials that - inexplicably - tried to foist westerns on space-addicted Generation X-Wing. Good luck with that one.
Less notably, the SPIDER-MAN one-shot was a spin-off from the weekly.