I've been absent a while and struggling to catch up, but had to say something for pug. Your situation sounds horrendous and hope you get the support you need quickly. Do you have any union cover at all?
I'm NHS too and saw an article today about my union fighting the maternity rights for someone (different situation) but if you are in that sort of role (which as you talk of management I don't know if you are) it's worth speaking to your rep asap for support.
If not, do you know any reps in your hospital who could point you in the right direction,or like someone else said, citizens advice?
Our service is being transferred to another NHS provider in October, it shouldn't change my mat leave but may impact my return to work arrangements, something to question at consultation (not that it will change anything, just helps to be forewarned!)
pug my understanding date wise you should be fine, 11th week before expected date is taken from the Sunday before due date then counted back (so for me due 20th Jan, it's the first Sunday in November) your year long contract not due to expire until after this date so it should be extended for mat leave. (if I've read all your info correctly!)