GazNicki
You can't appropriately split "reasonably practicable" into two separate words. The first word is an adverb that qualifies the adjective that follows.
So, there is plenty of case law on what is or is not "practicable" - in simple terms what is technically achievable.
"Reasonably practicable" is a less stringent qualfication, where it is necessary to balance the reduction in risk that would be achieved by putting a mitigation in place against the "time, money and effort" aka cost required.
Then depending on your choice of case law (1949 v 1954) you have to decide whether the cost is "grossly disproportionate" or simply "disproportionate".
Part of that balancing act would include taking into account the downsides of any mitigation which might include introducing a new risk, or, perhaps putting people at a disadvantage, or in other circumstances adversely impacting heritage, the environment etc etc etc.
So, in my view it is entirely appropriate to consider the potential breach of equalities legislation in deciding what is or is not "reasonably practicable".
As regards causation in this particular case, the reportage includes the assertion that the victim did NOT fall down the stairs but rather fall over the handrailing.
Assuming that the store is of relatively modern construction it will have been constructed to be 1100mm (or more) above the 1st Floor surface, with intermediate protection between top rail and floor level (all designed so as to make it somewhat difficult to climb and THEN fall over). All set out in one of the "Approved Documents" that support Building Regulations in England.
I can't think of a rational explanation as to why one would construct this edge protection to a different standard simply because one person is prone to epileptic seizures.
You would build the edge protection higher if those at risk might be e.g. cattle on a bridge crossing a road. See "DMRB".
We will probably never know the exact reasons why the Jury found Morrisons guilty on three charges as what is said in the Jury is supposed to be kept in the Jury room with a juror committing an offence if they take what is in the jury room and announce it beyond. (I've been there - fine for me to say that we found the two defendants not guilty of the charges of manslaughter against them, fine for me to point others to the media coverage, which might give a very good clue to what we the jurors thought, but not fine for me to explain WHY we came to our decision).
However, on the assumption that the Jury concluded that it was reasonably practicable for the victim's locker to be moved back to the Ground Floor, then it follows that whatever "personal" risk assessment Morrisons had done would fail if it did not include for such "reasonable adjustment".
BUT, this case is NOT an authoritative judgment - it has not been heard in an Appeal Court and we shouldn't read too much into it. May be the Jury came to an inappropriate decision. On the face of it, it seems easy to conclude that the victim's locker could have been put back on the Ground Floor, but we don't know what changes in store layout were made to include moving employees' lockers UPSTAIRS - possibly it was not practical (I am deliberately avoiding the words "reasonably practicable" which is the test) to put the locker back on the Ground Floor.
Quite possibly the defence was not as robust as it might have been. It's not uncommon in my experience for the lawyers working on the defence of a health and safety prosecution to be outside their comfort zone.