You can register with a GP without an address (rough sleepers can register with a GP) although some surgeries either don't know this or mislead patients by refusing to register them
You can receive hospital care without a GP
Please register with your GP tomorrow
Obtain an urgent appt (ask for an on the day emergency appt)
There are other things that need to be monitored in pregnancy eg blood pressure, not just scans
If your GP won't give you an appt I would go to the hospital Antenatal Day Unit (like an A&E for pregnant ladies), explain you haven't been able to obtain Antenatal care yet, and sit and wait to be seen
Most pregnancies are uncomplicated, but it would be a shame if you had a complication that could have been treated, so insist on seeing a doctor tomorrow
With breech, the obstetrician would usually offer to try and turn baby, and if not offer a caesarean section. In the uk most breech babies are born by planned caesarean, although vaginal birth is possible
If you get any symptoms of labour go to your nearest Labour Ward. Any woman in labour can turn up and receive care.
I can see you have been trying to get the best care for your baby with private scans. But it is unusual for somebody in the uk not to manage to access NHS care, I can see you were misled, but I am a bit concerned that you might be quite vulnerable to not manage to get past that initial poor advice iyswim? As in, I think your typical person would have inisisted/ gone to hospital/ sought more information online or from CAB to back them up etc. I can see you were trying your hardest, but it does sound like you might benefit from some extra support to help you navigate things for the rest of your pregnancy and when baby is born.
Best of luck speaking to your GP.
Oh - you should be feeling baby moving regularly now, if baby is moving less that is a reason to go to Labour Ward urgently, even if everything else seems well.