Some of the very good posts in this thread seem to have been missed out in amongst the discussion. Even under basic Civil law, it is very unlikely the requirements for you to face successful civil action ("be sued"). The Social Action, Responsibility and Heroism Act 2015, often colloquially referred to as the "Good Samaritan Act," as firstly pointed out in the post above by
@Horizon22, reduces this even further.
With regard to First Aid training; I think many people here are over-egging the benefits of this, or are perhaps unduly concerned at the lack of railway staff having this. There is no one such "First Aid training" course or qualification; this could be anything from the level 2 qualification which is probably the most common, often called "Emergency First Aid At Work" and is usually a halfday or one day course, or "First Aid At Work" which is level 3 and two or three days. There are also other courses out there such as fire warden training, sports first aid, mental health first aid, AED training and many more. And that's even before you take into account refresher courses.
Do you need to be trained to use the type of AED that you might find on a wall in a public place ? My understanding is that they come with 'no training required' instructions and will not shock unless the device detects the appropriate cardiac activity. No doubt training would help with confidence and significantly speed up the process.
I think your final sentence hits the nail on the head. I often see people in my role that during an incident seem to be suffering from adrenalin or something else that makes them incapable of carrying out fairly simple tasks or following instructions. Whilst an AED is very easy to use, and indeed contains both written and spoken automatic instructions, people in the "excitement" (probably a bad word to use) of a situation in which it's required, I can very easily imagine someone struggle to work it out themselves.
Back to the original question posed, railway staff will follow the instructions and policy of their employer. My company's policy is that a customer should always be removed from the train when ill, the exceptions being:
1. If you suspect a spinal injury, with the knowledge that this is extremely unlikely on a train
2. If the person is too large, or volatile to move, without possibly causing injury to yourself
3. If the person is in an active stage of a seizure
I often find the biggest barrier to implementing this procedure is people (not railway staff but other travellers) who have done some kind of first aid course where the advice is not to move someone, or to put someone in the recovery position. This might be fine in an office or restaurant, but isn't particularly good advice on a train. I've never had such a problem with a paramedic or trauma doctor, who understand the risks of working in a railway environment.
Such guidance is supported by the ambulance service -
https://www.whatdotheyknow.com/requ...erations 18March2013.pdf?cookie_passthrough=1