Given its general importance for studies of star formation at all redshifts, the issue of the heating mechanism for the warm/cool dust in luminous AGN is one of the key problems in extragalactic astrophysics. We propose to address this issue by using the unique high sensitivity capability of the Spitzer to make a mid- to far-IR (MFIR) photometric survey of a complete sample of luminous 2Jy radio galaxies and radio-loud quasars at intermediate redshifts. Radio-loud AGN are ideal for a study of this type, because they have relatively clean selection criteria and it is possible to determine the luminosity, orientation and age of the AGN using the emission line and radio properties of the sources. Moreover, an important advantage of the 2Jy sample is that, unlike any other major sample of powerful radio sources, deep optical spectra exist for all the sample objects. These spectra provide both accurate emission line luminosities and information about the stellar populations -- crucial for investigating the link between starbursts and the MFIR properties. By correlating the MFIR, radio and optical properties of the objects in the sample we will determine: (a) the dominant heating mechanism for the dust at different MFIR wavelengths; (b) the extent to which the far-IR colours depend on orientation to the line of sight; and (c) the evolution of the far-IR properties with the ages of the radio sources. This will be the first deep MFIR survey of a substantial sample of luminous AGN for which complete information on the stellar populations, AGN and jet properties already exists.