If the judge is satisfied that he has all of the information he requires, he'll pass sentence immediately. So, if you've already been interviewed by the probation service for a pre-sentencing report and your barrister has already submitted any character references (or will be submitting them on the day), sentence will be passed when you next appear before the court.
If the judge requires the submission of further information (particularly a report from the probation service), sentencing will be delayed (probably by a month or two). If the judge is unsure as to whether a custodial sentence will be passed, you might be bailed. However if (as seems more likely, based upon your post) the judge is certain that he'll pass a custodial sentence (but he hasn't yet decided how long it will be for) he'll send you straight to prison, 'on judge's remand', while awaiting formal sentencing.
Chris