Elsewhere it is normal to resign when you get an offer (conditional on references), not say you will resign at some point in the future but expect references to be provided in the future.
Assuming you don't work in the NHS and work somewhere where employers are not customarily asked for references before the person has resigned, that is why he is not happy. They are now in limbo, unable to recruit or plan and have someone with one foot out of the door but no sign of moving the other foot yet.
Stick to your guns, but perhaps just bear in mind that this may be seeming unreasonable and ridiculous to them, so perhaps stick to your guns in a nice apologetic way.
Hi, I have recently accepted a part time job with the NHS after my current employer refused to let me work flexibly after having my baby. I have only been back at work a few weeks and was lucky enough to get this new job really quickly. As some of you will know, with the NHS there are lots of checks that have to be made before you get your formal offer letter, such as DBS (CRB), occupational health and references. Out of courtesy I informed my employer that I had been offered a job with the NHS and that they would be getting a reference request through. Its an awkward situation because obviously I was informing them I was leaving but kind of saying "...but I'm not handing my notice in yet"! My director was apparently ok at the time (it was my line manager that told him), but has now turned (typical for him) and is now pestering me for a leave date and a resignation letter. I just don't know how to deal with it as it can take weeks for the checks to complete and it's advised not to hand in your notice until you receive a formal offer letter. He can be pretty brutal at times. Is he allowed to force me? Any ideas how I should deal with this? Thanks.