Just wanted to follow up my story for anyone who finds this thread in the future (or who was following it now -- and thanks to those who responded before).
Sadly my situation ended up with pretty much everything going wrong that could have, the classic intervention rollercoaster, though the irony was that I don't think the low-lying placenta was the cause of any of it, even though it definitely affected the treatment I got.
My hindwaters broke at 4am (Tuesday) at 40+1, with a small amount of bright red blood as well. Because of this, we went to the labour ward immediately, I was admitted, found to be 2cm and recommended to start antibiotics and induction right away. Both of which I declined initially preferring to wait for things to start on their own -- latent labour had begun already with mild contractions about 7min apart. Stayed the following day til midnight without much progress, very stressed due to the situation and how long it took to see anyone (cons and their teams took forever to see us), being cooped up in a labour room surrounded by other women in other rooms sounding like they were in hard labour. Finally discharged myself so I could go home and get some sleep, agreed to come back the next day for monitoring and more discussion.
Next day I saw my own cons who said he was fine with the very low infection risk but that because I still had a lot of forewaters (head was still high), cord prolapse was a concern and he wanted me to stay overnight. I did so this time, agreed to give it another 24 hours before induction and hoped for the best. Next day (Thurs) still not much progress, contractions getting slightly stronger but that's it. They broke my waters, had a moment when the midwife thought that the baby's hand was the cord (to be fair, she was pretty sure it wasn't, but it caused a major panic anyway). I was left to walk around for a few hours and see if I could get things going. Never really managed to do that, didn't get beyond 3cm and 3-4min mild contractions before finally giving in to the syntocinon drip early that evening.
The drip started ok and I thought I could manage without much pain relief (BIG MISTAKE), we got to 60ml/hr within 2 hours without much increase in contraction pain but also no more dilation. The cons came in and said "you have 2 more hours to get to at least 5cm" and left, cranking the drip up to 90ml/hr dose. Within 10 min I realised I was in big trouble without an epidural ready to go and upon finding out that an EMCS had all the anaesthetists busy and it would be 90 min before I could get one, I embarked on the worst 2 hours of my life. On the plus side I did get from 3cm to to 8cm in those 2 hours, on the minus side, without pain relief I was completely shattered and absolutely furious! The pain was so intense words cannot describe it.
At this point I finally got a mobile epidural which helped a lot, I managed to get to 10cm over the next couple of hours and got a much needed break from the stress and pain. Then was told to relax for an hour and "wait to push" despite starting to feel extreme urges to push. The top-up was wearing off so I asked for a half-dose more, thinking I still had lots of time for the pushing urge to come back... instead I was given 1 more hour to get the baby out. In the end I couldn't do it, she never got out of the pelvis and was slightly turned sideways and I had a choice between ventouse (and c-section if that failed) or just straight c-section. I chose the latter as I had lost all hope and at least I knew a c-section like this would be less emergency and more relaxed than one following a failed ventouse. Lived through another hour of hell as my baby was delivered, I felt completely empty and detached, hemorrhaged a bit due to the c-section, threw up from the injection of oxytocin, and didn't manage to hold my baby skin to skin for nearly 40 min after she was born. Thankfully my partner did a stellar job with her and with me and kept it all together. And all through this, not once was the baby in distress, she was absolutely fine from the second my waters broke 3 long days ago til she came out. 1-min Apgar score was 9, 5-min was 10.
So I'm now recovering from a c-section, but wondering if I could ever have birthed this baby naturally, or if the induction and associated stress was to blame for it. Baby is great, due to my fitness I'm recovering pretty well and was discharged after 48 hours from postnatal. I'm not angry anymore, just disappointed, but that's life. Sometimes you gamble and lose. Don't regret any decisions I made except maybe that I didn't start to push when I felt the urge to, and instead listened to the midwife to hold off. It was so frustrating to be told to push under a stressful time limit and just not be able to push hard enough.
Anyway, in the end my placenta was fine, it may have been that it was somehow keeping the baby from turning or getting out properly, or the placenta may have had nothing to do with that. I'll eventually pay to get a copy of all my notes so I can read through them and see if that sheds any light. Really wish my waters hadn't broken as they had so I could have given natural birth a real go, but who knows, maybe I would have failed to progress there as well.
Next time I'm hoping for homebirth VBAC, at least I know they can't induce me!
Hope this helps anyone who reads it. I know I've been helped by the many women who have shared their stories on Mumsnet so wanted to give my own story some closure.