UK- I've been in for one night only before - and it was the worst night of my entire life- that very fact has left me with such an awful memory - that I felt so much the worst after that experience
The bar is set pretty high in the UK to be formally sectioned,normally it's people who are severely psychotic and are a risk to themselves and others . It needs two doctors to agree to it as well as a specialist social worker, and beds are scarce.It costs quite a bit of money and after they feel you are well enough to be discharged from hospital you are legally entitled to support in the community which has to be funded by the local council.
The police can also section people ,the bar is set a bit lower here and the section doesn't last as long. The police detain you so you can be formally assessed by medical professionals.
There are two types of section medical professionals use, section 2 which is 72 hours and a section 3 which is where they can detain you for 3 months. But again it's rare.
A trick that was played on me though, as they got me to agree to an 'informal admission' to a MH unit ,promising me that if I wanted to leave I could, but while in hospital I tried to leave,and they said you can't until you see the duty doctor first, I was told by the doctor I couldn't leave and he would section me if he had to.
My advice if in the meeting they try the above trick, and start talking up the idea of an informal admission, refuse politely and calmly but express interest in working with the 'home treatment team'. That tactic got me out of it before. Once they think you are engaging with them they will in the end lose interest and leave you alone.