Well going by my online statement I should have £400+ in my account, but my available balance is actually considerably less, because although bills aren't yet showing up as paid on my statement, the money for them has been put to one side by the bank. You can only access the available balance, you can't touch the money that's in that inbetween stage. So for all intents and purposes, no that money isn't there. Your balance is £0 (oh I know that feeling ), you won't be able to get money out.
presumably the dd is due to be taken on the 1st of each month (?), so the monmey is set aside from the account on the 1st (today) but as it is not a banking day the actual transfer will take place on the next banking day (monday 3rd)
So that explains it if it is due out on the 1st if not then i have no idea!!!