The IEE Wiring Regulations (17th Edition), Table 4C1, page 268 shows rating factors for number of circuits or multicore cables. For single core, the table refers to 'Number of circuits', not "Number of Cables". The question is how do we address multiple (parallel cables) for a single circuit.
To explain in a different way, if three single core cables are used to supply a three phase circuit this is considered as one group. If six cables in parallel (two per phase) is used to supply the same circuit is this considered a single circuit for rating or two circuits. My reading of the table is that it should be one circuit (but I could be wrong).