Hi sheepcat, I had both my DSs in the labour ward of St Mary's so I can tell you about my experiences there!
DS1 (in mid-2009) I was overdue and had pre-eclampsia. I found that the lack of continuity of care probably contributed to my going into the ward too late (after contractions had been going on for 2 days and going nowhere) I had a long, unpleasant wait in the triage room (3 hours) and had to wait for an epidural (argh) On the plus side: the midwives, all of them, were great. the overnight one was friendly and helpful. was made to wait for switch-overs which was annoying e.g. I was ready to deliver by 7am on a Sunday morning but they made me wait to push until the new midwives at 8am.
DS2 (April 2011) i arrived at the triage room around 2am, was not checked immediately, eventually was told that i had to wait for a room as none were free! in the throes of second labour contractions, i knew i didn't have long and wanted a room so i could get an epidural. midwives few and far between, extremely unhelpful, and kept insisting they couldn't check my dilation as it hadn't yet been 4 hours since my first check (!?!) Horrible experience to be honest. had full labour in triage room full of other people. delivered DS2 20 mins after being given own room, with no pain relief (other than gas and air which had stopped doing anything ages ago anyway) midwives that delivered DS2 were new to me, and noted that the previous midwives hadn't made any notes about me overnight they didn't even know if my waters had broken or what way around the baby was facing when i was wheeled into the room!
My advice: like me, as an older mum and more likely to have complications, if you use the labour ward, bring a birth partner along who is vocal and prepared to push for you to get seen/get help/etc. -- some of the people are fine but sometimes things just don't move fast enough and you can run into some useless people (as i found overnight with DS2) I hope this isn't too negative, really trying to be helpful.
ps found the postnatal ward perfectly OK -- really, I wouldn't recommend going private for postnatal only! Good help, people checking in on you, etc.