I'm sure someone with a little in depth knowledge of the regs will provide and answer, but I am sure that after a certain height the ladders have to be tied off and so on....
but the guy is crazy, no way on this earth would I allow an employee to work at height off a ladder!
If it hits the fan, as an employer you will probably be for the high jump in a big way. If an accident should happen, and its a bad one, then you will be investigated, and if it is found that your employees breeched health and safety regs then you will be in it up to your neck for not ensuring that they abided by all the regulations.
This has nothing to do with the debate on WFP v ladders, for me it is a simple case of fear of prosecution!!
Ian