dani747, I understand - August born lad with developmental delays here (not prem but language development stalled for a year).
Bradford let us year-defer properly ie start him in reception at 5.0 (long story) and it has transformed his life-chances, for all the reasons you outline. He is thriving now and all of us (parents, teachers, nursery workers head, health professionals) just feel delighted with the (unanimous) decision we made.
Sir Jim Rose - mentioned above - came on mumsnet and, after great pressure, admitted that he had never meant there to be no exceptions to the rule.
Here in Bradford, you now need the support of professionals to year-defer. Find out how it is in your LEA (prepare to be fobbed off), see if you can enlist health professionals on your side and good luck to you. If you have made a firm decision not to apply for a school place I think that will help you. It was only after the deadlines had passed for the 1st intake year that Bradford realised I was deadly serious. Having foreign friends and relatives helped - they were all utterly disgusted by the English system. I would also have moved abroad had it come to that.
I do have confirmation from bradford that his education will be offset throughout his whole school career. But even if I found I had another fight on my hands to get him into year 7, not year 8, I would have no regrets.