The Government Says

Lowering the minimum train driver age to 18: rail industry implementation plan

Lowering the minimum train driver age to 18: rail industry implementation plan
Local copy of the-rail-industry-implementation-plan-for-lowering-minimum-train-driver-age.pdf

https://www.gov.uk/government/publications/lowering-the-minimum-train-driver-age-to-18-rail-industry-implementation-plan

seen at 14:42, 19 March in Policy papers and consultations.