Rather foolishly forgot to cross-check my photos with images of the species in question and turns out they appear to just be
Bombina bombina - thanks
@Prochilodus246 for pointing this out. Interestingly this species was (visibly) behind the scenes at London in previous years but was signed correctly as
B. bombina. This all raises the rather puzzling question of where the
B. microdeladigitora tag came from given those same toads have been at London for years and with correct signage. You'd imagine there must be frogs of that species at ZSL somewhere for that to happen - potentially a mix up or even a temporary swap?
In the meantime, apologies for the inadvertent misinformation

.