My current responsibilities at work include security checks for suspect items, and I also hold competencies for emergency protection and assistance protection (activities which tend to involve dets), as well as a host of other things which could be dangerous to my passengers, myself, and staff under my control, if not done properly.
I have in the past been required to also monitor the security of venues other than the railway (chiefly airport and major event security). These have been both paid and voluntary roles.
Sometimes I have had to make very difficult and unpopular decisions about security which have been correct, but also the inconvenient ones. Other times, I have been able to assess something as perfectly safe when it has been deemed too dangerous by everyone else. None of these decisions have yet resulted in death or injury.
So, credentials aside...
The HOT procedure in its fullest form is actually "HOTT" - Hidden, Obvious, Typical, Threat. The latter "T" is very pertinent to today's society. It is why security notices are thrown at train crew and other railway staff, to ensure they are aware of whether or not there is a specific and credible threat to railway infrastructure. This "Threat" assessment should really be at the start of "HOT", but "THOT" sounds a bit stupid. If a threat is not briefed out, the general protocol of HOT needs to be followed.
In other words, bearing in mind the threat, or not, the HOT part can be applied. This can be done from quite some distance and can be coupled to other checks related to people in the surrounding environment, and how they are behaving. The HOT assessment is theoretically so quick that you can do it whilst asking around if anyone owns the unattended item. This should be done in tandem.
The phrase "if you see something which doesn't look right", broadcast to the general public at admittedly incredible frequency, is really the whole protocol without giving it an acronym. The gut feeling of people who work in the railway environment is likely to be more accurate as a second opinion, which is why people are not encouraged to go around pushing passenger alarms and jumping out of trains, without the situation being assessed properly. Some passengers have reported the equipment boxes fitted under train seats (the sort of things which hold safety equipment isolation switches/cocks) as suspicious before - it just goes to show that the passenger is, unfortunately, not always right!
I believe the unexploded bomb on the Jubilee Line not so long ago was at least partially detected by the train driver carrying out the HOTT procedures. The "bag for death" on the District Line wasn't, as far as I know, reported to staff and as such nobody checked it; had it been checked, a paint pot in an insulated bag would hopefully have at least led to a check to see if anyone owned it, and if nobody came forward, then it's not a typical thing to leave completely unattended (nobody will have popped to the loo on a Tube train, decorators tend to need their work equipment with them, etc. etc.), so... there you go!
If it's deemed suspicious it doesn't need to be touched unless you are specifically trained to do so.
As for detonators and the like...
There is an element of personal risk with any work on or near the line, especially when you could be confused (or injured) in the event of an emergency. In a third rail area, for example, a driver with a head injury might be confused but may still struggle out of their cab with the little yellow box of dets or track circuit clips, still try to put them on the line, and end up trying to clip them onto the third rail, which could have devastating consequences to them, as well as risking an impact still occurring from another train.
In reality, if you did actually have to do emergency protection, it would probably prove far more risky than assessing most suspect packages, even in the world of IS (or post-IS) threats and suchlike.
I haven't seen any evidence to directly compare the risk to a driver from incorrectly working on the line in an emergency, compared to the risk of getting too close to an item and it exploding before they could do the HOTT procedure. But both are so rare that every attempt should be made to both protect trains in failure or accidents, and also to assess anything which could be a suspect item. I believe both tasks are more likely to do some good than not.
As for whether drivers should be trained in assessing suspicious items - of course they should be - and many are, often now as part of their induction into a company, and/or as refresher training. A train driver may not work in the saloon, but they know their train inside out, how to get other staff to assist, and what typical passenger behaviour is like on the platform, which could dictate whether something carried is typical or suspicious or not.
One final point about HOTT. It is entirely correct to suggest that one benefit of these checks is to avoid unnecessary evacuations. Evacuations might seem like a failsafe last resort, but in reality they do not always result in a safer situation. Full evacuation of major transport premises generally causes so many crowd control issues - which in turn can result in stampedes, huge traffic control and safety issues in the surroundings, confusion and distress, and economic damage - that it should only be a last resort. Trains are even worse, if they're away from stations!