Ultimately, when it comes to labour and birth they can say a lot of things, but there truly is no "allow" about it; all they can do is advise you on what *they* would prefer and inform you on what they feel is safest.... it is still totally up to you how & where you give birth and they really cannot force you to do do something you aren't happy with.
I'm not sure I'd quite agree with that... as if it is a hospital birth and she is told her BMI is too high for a water birth, she can ask and ask and ask all she wants; they don't have to get the birthing pool out and ready.
You have the right to labour and birth how YOU want. And if you don't like what you are being told, you have the right to get a second opinion, or speak to a different consultant, or the Supervisor of Midwives.
I'm not for one minute advocating doing something inherently dangerous, HOWEVER, if the
*only* reason you are being "denied" a water birth is because your BMI is one or two points over the "magic" cut off, you are within your rights to insist on one anyway and unless there is a genuine reason why it would not be wise, they are not allowed to refuse you.
You know how mobile you are. If you feel safe to labour in water and agile enough to get in or out as needed, then simply having a slightly higher BMI should not be an issue (providing all other factors like BP etc are normal).
No one should go into labour thinking their midwife (or consultant) gets to dictate how or where they give birth, it doesn't work like that, even if some HCPs like you to think it is.
It's still your birth and you are still able to form your own opinion. If you truly feel their way is safest then you can do it their way, but if you feel your way is just as safe, they really have no right to refuse to follow your wishes.