I would tend to agree with the scenario you present and your conclusions, but....

What if our burglar was instead a child or young person of limited mental capacity, or a group of kids breaking in for a laugh? What if these break ins were a regular occurrence so the owner was well aware of the tendency for children to do this? What if this was a low tier COMAH site and they had elected to lock the fire doors as a cost saving measure instead of hiring security guards and erecting a decent fence? What if the fire was started due to negligence on the part of the owner in failing to address known fire risks?

Context is everything in these discussions and certainly would be in the courts. Just because someone is trespassing does not necessarily absolve the owner/operator of responsibility.

Unless you have permission or implied permission to enter a property it is trespass. Implied permission is given for deliveries, postman, customers etc. By leaving a door or window open does not give anyone implied permission. The duty of care to trespassers is covered in the Occupiers' Liability Act 1984.

Therefore if a burglar, who as well as trespassing is breaking criminal law by attempting to steal something, dies there is no case to answer unless gross negligence involved. Locking a fire door of an empty property is not gross negligence. Gross negligence would involve not controlling imminent, foreseeable and real risks for example storing large quantities of petrol dangerously in breach PCR and DSEAR, which was inadvertently ignited by the burglar.

The real concern for me would be getting the corpse removed fast, to start repairs and re-open the biz.
Then consulting solicitors to see if the deceased persons estate could be sued for damages.

Ray of course why didn't I see that, happens all the time ?

But wouldn't quote "and the candle inadvertently ignited a vat of oil" have actually put the candle out. I would not have thought you would be able to ignite a vat of oil like that. Does oil give off flammable vapour at room temp ? Not enough energy in a candle to heat the oil sufficiently to raise its temp is there ? Maybe if there was something in the oil to act as a wick ? (swag bag for instance ?) :0)

Me too. This matter is quite simple that an intruder is not a 'relevant person' so the RP has no duty to protect them. This is why final fire exits can be locked at night

I understand that the term relevant person applies in Scotland too however I am not sure if the definition excludes intruders in the same way the FSO does

Why on earth would you want to padlock a fire door in the first place. Get all you deserve if you do.

Literally thousands of premises in London alone secure final fire exit doors after business closes. Those with large occupancies such as department stores, theatres and nightclubs require panic bolt (push bar) door furniture as a result of their FRA to ensure relevant persons can escape without a crush situation developing

It is these premises that may be most vulnerable to intruders as these doors are rarely secure enough to satisfy businesses or their insurance companies.

I have worked with many premises to ensure they have adequate systems to ensure doors are unlocked or chains removed before the building is occupied

If managed appropriately there is absolutely no legislative issue in securing a premises out of hours. I am surprised anyone would query it to be honest as the days of leaving the back door open when you pop out are well behind us!!