Their role is to provide routine antenatal care and to deliver the baby in a normal delivery with no complications. They even provide home births if you want one and you are low risk. For a first baby you can expect 10 midwife appointments throughout your pregnancy. They deal with routine blood and urine testing, blood pressure, health advice, listening to the heartbeat, measuring the bump etc. They will refer you to the hospital if you have complications that need further monitoring from a doctor.
You will have two normal ultrasound scans - one at 12 weeks (dating and downs screening) and one at 20 weeks. However there are loads and loads of private ultrasound clinics in the UK which do extra scans and 3d as these are becoming very popular here.
As soon as you arrive in the country and are moved in, get registered at a GP immediately and tell them you are pregnant after fertility treatment and need a quick referral to the midwife. By November you should be in your 2nd trimester surely so you will probably have had some monitoring in the US before you leave.
After the 12 weeks scan here, the next appointment for most people is 16 weeks with the midwife.
In most areas you can choose the hospital where you want to give birth and can even change your mind/make your decision later on in pregnancy. Most of us live in places with only the one hospital nearby but you might have more choice in London, so you can find out when you can visit the maternity ward to get a feel for which you are happiest with.