BREWERDAVE1: am I paranoid?
OK, I just made that quote up. You are right, the apparent balance will look worse before/better after the DD collection, however AIUI monthly payment recalculations are only done once a year. Perhaps other suppliers online billing has moved on also but the SP online billing system is the best I have come across.
I am confident that as long as the monthly payment is right for the year a meter reading submission won't result in an adverse DD recalculation. Actually if it was well out I think it would not be unreasonable for the supplier to amend it. The only issue would be whether it was a reasonable and accurate recalculation.
I provided an unsolicited meter reading a few days ago, just after DD time of course. I noticed this resulted in the next scheduled bill date moving from the previous scheduled date to 3 months hence. I know my payments are right for the year but over the winter I have been behind but reducing at each meter reading. So far no attempt to up my DD.
I am happy to recommend SP online. In most areas they also happen to the cheapest supplier with no sneaky "gotchas" such as Npower's discount deferred for 12 months or E.on's no discount on final bill.