Neil, I take it from the picture that the windows with the cross bar in open at the top and the middle whole pane section does'nt. Providing the top openers open wide enough to lean out it should be ok to lean out and mop n blade them ( the inside ledge looks sturdy enough to stand or kneel on). Or are there other problem windows that are not so easy to do ?
I've cleaned an apartment on the 25th floor this way in the past.
Simon