The A61 Appointed Person CPCS is the industry "gold" standard - I hold one and it's an extremely difficult ticket to get.
But it's not an actual legal requirement - I train an equivalent for example - mine isn't CPCS accredited, but contains the same elements. CPCS would have you believe that their qualifications are the only ones that hold water - but that isn't so.
Training to a good standard is what's required as part of the overall criteria for competency.
Part of any AP course should be the base calculations for loading and sizing of outrigger pads and the calculations to de rate slinging systems based on the slinging arrangement/included angle of the slings. It should also cover a myriad of other things such as crane stability, proximity hazards, how cranes work, duty charts, falls of line calculations etc.
In all it's a complicated job and not to be taken lightly - a surefire way to get onto HSE's radar is to turn over a crane - especially a big one......