I'm a British citizen living outside UK & never lived in it.
I got my citizen ship by descending from my mother
if I come to UK to get birth to have the citizen ship for my baby , what are the requirements for obtaining my NHS number to go to my GP? & how long it takes?
( I still don't have an address in UK but i think i will rent home when i come)

You’ll be allocated a NHS number when you register with a GP if you do not already have one.

https://www.nhs.uk/nhs-services/gps/...-a-gp-surgery/

Whereabouts are you moving to? The rental market in a lot of the UK is red hot, so you’ll need a job first usually to be in with a chance. Make sure you bring references, and be prepared for a short term rental or hotel stay to start with until you can find something for longer term. You’ll also need to have accommodation lined up for your husband’s visa application too.

As long as you’re moving permanently (i.e. not just to have the baby) then you’ll be covered by the NHS from arrival.

I'm not 100% sure but I think I'll move to London or Manchester
what is the references i have to bring with me plz?
and what are the documents that prove i will move permanently not just for having the baby?

If YOU are a Brit citizen, you don't need any references to move to the UK.
You WILL need proof that you are living in the UK (tenancy agreement to prove permanent place of accommodation/paylips to prove job/bank accounts etc) and not just visiting for the birth in order to use the NHS.

When I moved back in 2016 I had to produce my British Passport (proof of right to live here) and also a utility bill or similar to prove that I was resident. My very old NHS number was not recognized and I was issued a new one.

A year later when I attended hospital for the first time I also had to produce passport and utility bill.

I think it will vary among NHS trusts on how strictly they implement this requirement.

I meant references for rental applications - i.e. from previous landlords. I’m guessing that London and Manchester are pretty hot rental markets. You won’t have a credit score for quite some time, so that will be a negative for landlords, so whatever you can provide to give yourself the best chance if you’re one of 20+ applicants for each property would be helpful.

Will you be moving ahead of your husband or will you be able to apply for his visa without a job in the UK? If you’re moving ahead and will have 6 months or more of payslips by the time you come to look for a family rental, that will help.

Here's a link to a website that might help clarify the situation
https://maternityaction.org.uk/advic...ad-in-england/
Note this is for England. Might be different in other countries.

You'll see it refers to being "ordinarily resident" in order touse NHS for free. There's no exact legal definition with regard to this because Parliament has never passed a law to state this. Instead there have been a series of court cases that have established Common Law precedents. On the gov.uk website there's a long explanation of how NHS trusts can decide if a person is "ordinarily resident".
https://www.gov.uk/government/public...d-purpose-tool

if i probably will set with a friend can i register with GP with my friend address?
with a letter from the homeowner (my friend) to GP that i resides at this address

This is what we did for our son - a letter from us that he lived at our address plus a copy of one our utility bills proving we lived at that address. That letter also worked for him when opening a bank account and also applying for his NI number. If such a letter works for a relative then I would think it would work for a friend.

When our daughter moved back and lived with us for a few months then we added her to our utility bill.

your son was living outside of UK?

We were all living in the USA from 1987 until my wife and I returned in 2016. Our son moved back 18 months later and then our daughter moved back in 2021.

If you’re living there then you’ll have proof of that - car insurance with the address on, bank statements, bills, your name on the council tax bill etc? So even if you’re not paying her rent you’ll still have evidence, make sure you take that in addition to a letter from her.

And if you’re using that address for your husband’s spouse visa there are different requirements so make sure you’re aware of those too.

Just having a letter from a friend saying you live at the address, does not prove you have permanent residency in the UK - this will not suffice if you think this make you eligible for NHS maternity services.