Basically I don’t recommend accessing a flat roof from a ladder
Why?
It sounds like the bizarre recommendations of someone sat behind a desk with no hands on experience who has been appointed to 'baby-sit' those who know better. Reminds me of the H&S documentary that was on the box about a year or so ago where the H&S guy was demonstrating how to climb a set of steps. He got to the top rung and bashed his bonce on the ceiling.
He knew exactly what he was doing obviously. Yet they are appointed to oversee us, they havent got a clue.
Flat roofs are accessed hundreds of thousands of times daily by window cleaners, painters, builders, flat-roofers with no accidents to report. Of course there are going to be accidents but there are also accidents on roads it doesnt stop you driving does it?
Accessing flat roofs is fine just dont be dumb in the manner that you go about it.