Thanks Pete, very helpful.
Appreciate agencies are likely to be a bit random with the work. But your idea of smaller operators is good - almost like their relief driver or something. Don’t want to run before I can walk, but no point in learning to walk if you can’t run a marathon one day! 
LTD good, as I can choose when to take a salary, the missus can have one too for looking pretty etc. All about (legitimately) minimising that tax bill!