In fact, you even still accrue vacation time while off sick, I was off sick for a year and when I came back HR came to me with the news that I had extra holiday to use the next year because it been rolled over from when I was off sick.
If you're sick while on holiday you can even try to claim the days back although most people don't as that's seen as taking the piss a bit.
But in general you will be paid full wages for intermittent sickness (ie three days -> couple of weeks)
As you are sectioned you will have a doctor's note by default, so there is no chance of being fired. (employment tribunal will back you up on that. However there is a cost(capped at £750) to that nowadays [thanks david cameron, you utter shitfacewankstain])
There are a number of rights for returning to work as well after a long sickness.
Should that fail, there is still nominally a safteynet of universal credit. However that has become rather inhumane recently (thanks again David you shitbag.) but it is not as inhumane as unemployment insurance in the US.
The Samaritans hotline (a general distress helpline) is there to listen. Nothing else. They do not provide treatment, judgement or the like. Sometimes that is enough. More importantly its anonymous. You will not be sectioned by phoning them
To be sectioned (ie detained against your will), you _have_ to be assessed by a doctor within 24 hours. You need to be deemed a risk to yourself or others(by at least two doctors) before you can be held any longer.
You cannot be fired for being sectioned in the UK.
So whilst the UK is very far from being perfect in terms of mental health (lord knows we have a multitude of problems, some alluded to in the article) it is not as bad as described in the parent thread.