I don't think it means "Thou shalt not have a footed ladder, as a self employed person"
What it's saying is "Self employed persons, by definition, are mainly lone workers, so there is nobody, [usually], available to foot the ladder"
Whoever writ this, has not read it out aloud, probably he has read it to himself; and because he knows what he meant to say, he thinks everyone else does!
Demonstrates two points really
a Always get somebody else to read wot you writ, [when I was writing training manuals for BT, it was called "idiot testing"], and you tried it out on several idiots!
b Younger HSE staff are being employed, and they are suffering from the decline in educational standards that is prevalent nowadays, and are less capable of structuring English grammar.
Baldeagle