  During the 2014 HST/Swift and ground-based multi-wavelength monitoring
campaign of NGC 5548 (AGN STORM), the UV-optical broad emission lines exhibited
anomalous, decorrelated behaviour relative to the far-UV continuum flux
variability. Here, we use key diagnostic emission lines (Ly-alpha and He II)
for this campaign to infer a proxy for the all important, variable driving EUV
continuum incident upon BLR clouds. The inferred driving continuum provides a
crucial step towards the recovery of the broad emission line response functions
in this AGN. In particular, the ionising continuum seen by the BLR was weaker
and softer during the anomalous period than during the first third of the
campaign, and apparently less variable than exhibited by the far-UV continuum.
We also report the first evidence for anomalous behaviour in the longer
wavelength (relative to 1157A) continuum bands. This is corroborative evidence
that a significant contribution to the variable UV-optical continuum emission
arises from a diffuse continuum emanating from the same gas that emits the
broad emission lines.
