Just passing this on in case it applies to anyone else or is of any use.
I normally (of late) receive my bill at the beginning of each month and go to the post office to pay it.
So far this month, I haven't received one.
I went to the Endesa Service Point in the local leccy shop and armed with an old bill, the lass printed one off for me.  So far so good.
When I looked at it, I realised that the amount was much smaller than usual and in fact comprised only the fixed standing charges.  There was nothing for consumption and the meter readings were both estimated and the same reading (which of course adds up to zero).  Of late, since the start of monthly billing, they've been doing an estimate and an actual read on alternate months.
After much punting around, I managed to get hold of a nice lady on the phone who claimed she didn't speak English and then proceeded to conduct the remainder of the converstaion in said language.  (Priceless aren't they ?).
She reckons as a result of the new system where we had the choice to change to a new supplier (rather not thanks, having experienced npower et al in the past), that the August bills will be sent out as normal and will comprise the fixed charges for August plus consumption for both months.