It would still be useful to know where you got that impression? If you have discovered the Citizens Advice page on the subject, well let's just say I think it could be worded much better.
The fact is that anyone "ordinarily resident" in the UK is entitled to use the NHS for free. This is better described on
this webpage. Although headed about Primary Care Services, the same rules apply to hospital treatment.
So it comes down to whether the person is "ordinarily resident" in the UK. I think it can be argued very strongly that someone in the UK on a fiancée visa, who fully intends to get married in the UK, and then apply for spouse visa in the UK, and live with their spouse on a permanent basis, is "ordinarily resident" as soon as they arrive.
After all, someone coming here on an employment visa, either WP or HSMP, is covered as soon as they arrive, even before they start any work.
