Hi Smyys,
I moved to London from the US when I was 6 months pregnant. I agree with much of what's already been said, but the finer details do often depend on your area. Here in SW London, for example, postnatal services seem really stretched. I just got one home visit from a midwife (the day after returning from hospital), and one home visit from a Health Visitor (a week or so later, IIRC). Other routine postnatal checkups were done at a local clinic.
My prenatal checkups alternated between a GP and a midwife, every 2 weeks for the 3rd trimester. My local GP surgery and midwife team was quite big, and I almost never saw the same person twice.
I found that the NHS pre- and post-natal care was very... I can't think of the right word... uniformly structured? Everyone has the same packet of notes, every appointment is written up on a specific form, everything is signed off with the right box ticked. I had a routine pregnancy and during appointments the midwives spent more time filling in my paperwork than they did actually looking at me.
In contrast to this, though, was the incredibly Byzantine network of midwife teams and maternity units and GPs and Health Visitors. 'Midwife team A is based at hospital B and operates a clinic at GP surgeries C, D and E every second Monday'... 'your Health Visitor team are reachable on this number or at drop-in sessions at the local community college from 9-12 on Fridays''.... I sort of trundled through it in a daze. I always knew when and where to go for my next appointment, but that was about it.
It was generally fine, but not very personal, and sometimes frustrating; whichever practitioner you're seeing each time rarely has time to read through your bundle of notes, so they end up asking you the same questions over and over. I must've been asked at every appointment 'have you had your whooping cough vaccination?'. Not a big deal, but what's the point in filling out all those forms in triplicate if no one really gets a chance to read them? I expect it's more about forming a papertrail in case anything goes awry, but I did miss having a single OB-GYN who oversaw my entire pregnancy.
Given the whole structured approach thing, be prepared to explain over and over why you're 'booking in' so late (your 'booking' appointment is your first, usually at 8-12 weeks, and involves them taking a medical history and blood tests etc). What with registration faff and whatnot, I didn't actually 'book in' until 28 weeks, and since this meant that a good portion of my notes were blank then I was often asked about it at appointments. Not in a bad way; it's just unusual, I suppose.
I brought all my medical notes from the US, but no one was very interested in them, and I had to have my basic blood-tests redone, and also have another ultrasound scan when I booked in (despite already having had 3 in America: dating, nuchal, and 20-week).
Good luck! Registering with and seeing a GP will set everything into motion, so, as others have said, make that a priority as soon as you arrive.