  We have measured the wavelength-dependent lags between the X-ray, UV and
optical bands in the high accretion rate ($L/L_{\rm Edd}\approx40\%$) Active
Galactic Nucleus Mrk 110 during two intensive monitoring campaigns in February
and September 2019. We divide the observations into three intervals with
different X-ray luminosities. The first interval, already published in
Vincentelli et al. (2021), has the lowest X-ray luminosity and did not exhibit
the U-band excess positive lag, or the X-ray excess negative lag that is seen
in most AGN. However, these excess lags are seen in the two subsequent
intervals of higher X-ray luminosity. Although the data are limited, the excess
lags appear to scale with X-ray luminosity. Our modelling shows that lags
expected from reprocessing of X-rays by the accretion disc vary hardly at all
with increasing luminosity. Therefore, as the U-band excess almost certainly
arises from Balmer continuum emission from the broad line region (BLR), we
attribute these lag changes to changes in the contribution from the BLR. The
change is easily explained by the usual increase in the inner radius of the BLR
with increasing ionising luminosity.
