This is the first paper of a series exploring the multi-frequency properties of a sample of eleven nearby low excitation radio galaxies ( LERGs ) in the southern sky . We are conducting an extensive study of different galaxy components ( stars , warm and cold gas , radio jets ) with the aim of improving our understanding of the AGN fuelling/feedback cycle in LERGs . We present ALMA Band 6 ^ { 12 } CO ( 2-1 ) and continuum observations of nine sources . Continuum emission from the radio cores was detected in all objects . Six sources also show mm emission from jets on kpc/sub-kpc scales . The jet structures are very similar at mm and cm wavelengths . We conclude that synchrotron emission associated with the radio jets dominates the continuum spectra up to 230 GHz . The ^ { 12 } CO ( 2-1 ) line was detected in emission in six out of nine objects , with molecular gas masses ranging from 2 \times 10 ^ { 7 } to 2 \times 10 ^ { 10 } M _ { \odot } . The CO detections show disc-like structures on scales from \approx 0.2 to \approx 10 kpc . In one case ( NGC 3100 ) the CO disc presents some asymmetries and is disrupted in the direction of the northern radio jet , indicating a possible jet/disc interaction . In IC 4296 , CO is detected in absorption against the radio core as well as in emission . In four of the six galaxies with CO detections , the gas rotation axes are roughly parallel to the radio jets in projection ; the remaining two cases show large misalignments . In those objects where optical imaging is available , dust and CO appear to be co-spatial .