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We present the results of a continuum reverberation mapping study of theradio-quiet Seyfert 1 galaxy IRAS 09149-6206. The analysis was performed usingX-ray, UV and optical observations made with the {\em Swift} telescope betweenJanuary and December 2017. The time delays between different light curves weremeasured using three different algorithms: PyI$^2$CCF, PyROA and JAVELIN. Ourresults show that the time delays increase with wavelength after $\tau\propto\lambda^{4/3}$, as predicted for a geometrically thin and optically thickaccretion disc, but only after accounting for significant diffuse continuumemission from the broad line region. However, the measured size of theaccretion disc can be up to five times larger than that predicted by standardtheory. To our surprise, the strong increase in soft X-ray fluxes is delayed byabout 15 days compared to the optical UV fluctuations, which challenges theprediction of the lamp-post model. Our analysis of the X-ray variabilityreveals the presence of a non-variable spectral component at 0.3-6.0 keV alongwith variable excess emission at 2.0-3.0 keV, which could be partly related torelativistic reflection in the inner region of the accretion disc. IRAS09149-6206 joins the list of objects for which the traditional lamp-post modelcannot explain the observed time delays. A scenario that incorporates othergeometric considerations into the lamp-post model, e.g. an extended coronaalong a scattering source, might be better suited to explain the observed longtime delays

On the nature of the continuum reverberation of X-ray/UV and optical emission of IRAS 09149-6206