That Custody Sergeant was indeed issuing threats not offering help with his reference to sectioning.
Of course, had Ms Farrow not changed her answer, he’d have been a bit stuck. As this helpful guide from Mind explains (emphases mine):
A police station can only be used as a place of safety if your behaviour poses an imminent risk of serious injury or death to yourself or another person. The decision must be authorised by an inspector after consulting with a registered medical practitioner, a registered nurse, an appropriate healthcare practitioner, an occupational therapist or a paramedic.
So, while no warrant is required for an S136 & she was in a location where it can be enacted, a potential anxiety disorder (am unclear as to whether this is diagnosed/was declared to the police) wouldn’t meet the “appear to have a mental disorder” threshold; & expressing an inclination towards self-harm is worlds away from “in need of immediate care or control”. The police officers do not, themselves, have the power to section, it is always a decision made by clinicians.
As Caroline was leaving when she was asked, there is no excuse for the attempt to use the police station as a place of safety, either: A police station can only be used as a place of safety if your behaviour poses an imminent risk of serious injury or death to yourself or another person.
The police must review at least hourly (or every three hours if you’re asleep)
whether you still need to be kept at a police station rather than some other place of safety. If you no longer need to be at a police station they should transfer you to another place.
If there had been genuine concern for Caroline’s wellbeing they could have enacted a S136 at the nearest hospital or even at her home - or the home of a willing friend. Threatening to lock her back up was exactly that - threatening to lock her back up.
It suggests quite heavily to me a failure to adequately complete the necessary risk assessment (as per PACE Code C) - at no point while Caroline was being held did they consider that risk much less take additional steps to mitigate against it; so on finally asking her she was threatened into changing her answer.
Tangentially connected, but I’ve always found it fascinating Dante only gave the 8th Circle of Hell - where those who’ve committed fraud (not in the modern sense, but any kind of deception to benefit themselves) reside - an actual name. The Malebolge, or Evil Ditches. So Dante would have people deliberately making false reports spending an eternity aflame, I think, though I don’t know if he had any scope for multiple torments - they just wandered about, IIRC, so I suppose one of the stabby demons might impale them every now & then.