Do freelance lorry drivers need a limited comany?

I have recently been approached by several lorry drivers who variously want to be self employed (this is to do with the working time directive) but have come up with a snag that agencies want touch them unless they are a ltd co. They say it is to do with tax liability. Several agencies are trying to push them into a sort of "franchise" which appears to cream their profits and they don't like that idea. Any suggestions please
John Barratt