The Office of Road and Rail show that, in the quarter July to September 2025 4,105,000,000 net tonne (i.e., about 16,400,000,000 net tonne-kilometres annually) - kilometres of freight were moved by rail - about 8% of total freight moved. Is that really a 'handful?'
If most of this were, as you seem to wish, transferred to road, I wonder how much rail subsidy would be saved, and how this compares to the increased road maintenance costs incurred by those extra maximum-capacity artic. lorries. What would be the effect on road congestion, I wonder. Freight trains rarely kill or injure members of the general public, but that volume of extra road freight traffic might also increase the number of people killed or seriously injured in rad accidents.
But perhaps it's just possible that part of Network Rail's subsidy is, indeed, to 'provide for FOCs to run for a handful of trains', and someone in government has thought things through.