  We present the results of a continuum reverberation mapping study of the
radio-quiet Seyfert 1 galaxy IRAS 09149-6206. The analysis was performed using
X-ray, UV and optical observations made with the {\em Swift} telescope between
January and December 2017. The time delays between different light curves were
measured using three different algorithms: PyI$^2$CCF, PyROA and JAVELIN. Our
results show that the time delays increase with wavelength after $\tau\propto
\lambda^{4/3}$, as predicted for a geometrically thin and optically thick
accretion disc, but only after accounting for significant diffuse continuum
emission from the broad line region. However, the measured size of the
accretion disc can be up to five times larger than that predicted by standard
theory. To our surprise, the strong increase in soft X-ray fluxes is delayed by
about 15 days compared to the optical UV fluctuations, which challenges the
prediction of the lamp-post model. Our analysis of the X-ray variability
reveals the presence of a non-variable spectral component at 0.3-6.0 keV along
with variable excess emission at 2.0-3.0 keV, which could be partly related to
relativistic reflection in the inner region of the accretion disc. IRAS
09149-6206 joins the list of objects for which the traditional lamp-post model
cannot explain the observed time delays. A scenario that incorporates other
geometric considerations into the lamp-post model, e.g. an extended corona
along a scattering source, might be better suited to explain the observed long
time delays
