If there is a drought order then yes you can use ladders
Unfortunately, no you can't.
Although the water companies would have no objection to the use of ladders and bucket for window cleaning, the WAH regs would be breached if you did a job from ladders that you have previously done with WFP.
Sched 6 of the regulations spell out the exact circumstances when it is permissable to use ladders, and "drought order" is not one of them.
This is the very reason why Southern Water (unlike Sutton & SE Surrey Water) did not argue that window cleaners could go back to using ladders. After a risk assessment has concluded that WFP can be used for a particular building (or better yet, you have demonstrated by use that that the building can be done with WFP), using ladders is then in breach of the regulations.
This being the case, the DEFRA inspector who chaired the drought order hearing is likely to recommend a change in the wording of future drought order applications.
Instead, Southern Water concluded that water should be transported in if it were restricted.
The secretary of state has not yet ruled on the exact terms of the drought order, and having attended all of the hearings I am hopeful that the WAH regs will lead to a special dispensation for window cleaners.
It is also important to note that even if no dispensation is granted, WFP will not be affected until Phase 3 of the drought order. The water companies made clear that if Phase 3 is necessary, the situation would be extremely serious and would almost certainly be followed by an emergency drought order (meaning standpipes etc). They do not anticipate it will be necessary to engage phase 3, especially as average rainfall for the south east appears to be returning to normal now (March was the first month with "normal" rainfall for 14 months).
Even with all of that, there are some very simple measures window cleaners can take to make sure that they comply legally with the drought order, whatever form it may take, and continue to use WFP.
-Philip