Generation of Runaway Electrons during plasma disruptions, and their potential impact on the plasma facing components, is of great concern for ITER and future reactors based on the tokamak concept. The STEP (Spherical Tokamak for Energy Production) programme aims at producing net energy from a prototype fusion energy plant. At its current design point, the plasma current is higher than 20 MA and it is expected to be in the seed-insensitive regime of avalanche multiplication, i.e., any runaway seed would quickly generate a large runaway beam during unmitigated disruption current quenches (as in ITER and SPARC). This is confirmed by modelling runaway electron generation in an unmitigated disruption current quench for the STEP preferred concept flat top operating point, using the state-of-the-art code DREAM.