I start work at 5am every day that aint the issue what im looking for is if anyone knows the legal side of what can and can't be done.
It is if there is an accident and your the one stood in the middle of the road. The whole shabang will be the issue then. You, your insurance cover, your liability.
As Stu says, dont ask window cleaners, ask the highways agency.
Years ago I went on a coning course when we used to cone off lanes on a dual-carriageway (it wasnt for window cleaning) and there are laws, regularions, recommendations that you wouldnt believe.
Just for starters, a couple of cones as already suggested is nowhere near what you need. You need to start coning off a lane at particular distances, depending on what type of road it is and speed restrictions, you need to have cones spaced at certain distances, you may well need signing (Men At Work).............it goes on.
Get some proper advice, dont ask a bunch of numbnut shiners at midnight after kicking out time.
Otherwise you are uninsured.