Personally I am quite surprised that anyone is operating a system where 5 - 10 Kg of product is filled in a box that an operator then has to manually move to a nearby pallet. Humans may be cheaper than robots but cost should never prohibit effective health & safety especially for repetitive manual tasks.

The reality of that manual handling chart is that moving from mid-point and twisting / lowering to ground level even a bag of sugar is actually wrong for two "good" arms.

As to the FLT access is this based upon a three points of contact rule? Remember the Equalty Act requires suitable adjustment. If they have weakness in one arm but can still mount the truck perhaps it is the rules which need adjustment?

Never presume - always involve the individual to determine what they can and cannot do (a manager making pretend will never stand up in court) the assessment will then write itself including consideration of suitable periods of adjustment for the individual. The human body is remarkable in overcoming limitation and one weakness can often develop in to an overall strength.

Hopefully the injury was not work related, if it was prematurely pushing them from employment will add to their claim.