  We present Hubble Space Telescope (HST) infrared images of four gravitational
lens systems from the JVAS/CLASS gravitational lens survey and compare the new
infrared HST pictures with previously published WFPC2 HST optical images and
radio maps. Apart from the wealth of information that we get from the flux
ratios and accurate positions and separations of the components of the lens
systems that we can use as inputs for better constraints on the lens models we
are able to discriminate between reddening and optical/radio microlensing as
the possible cause of differences observed in the flux ratios of the components
across the three wavelength bands. Substantial reddening has been known to be
present in the lens system B1600+434 and has been further confirmed by the
present infrared data. In the two systems B0712+472 and B1030+074 microlensing
has been pinpointed down as the main cause of the flux ratio discrepancy both
in the optical/infrared and in the radio, the radio possibly caused by the
substructure revealed in the lensing galaxies. In B0218+357 however the results
are still not conclusive. If we are actually seeing the two "true" components
of the lens system then the flux ratio differences are attributed to a
combination of microlensing and reddening or alternatively due to some
variability in at least one of the images. Otherwise the second "true"
component of B0218+357 maybe completely absorbed by a molecular cloud and the
anomalous flux density ratios and large difference in separation between the
optical/infrared and radio that we see can be explained by emission from either
a foreground object or from part of the lensing galaxy.
