Azeebp
One of the problems here is that HSE can't make its mind up.
As Steve has pointed out HSE gives advice on RIDDOR reportability - so generally NOT reportable even if relevant thresholds are met.
However, in contrast, HSE recognises that the scope of HSWA does not exclude mental illness that is work-related and long ago published guidance on managing the risks including its "Stress Management Standards".
What HSE seems to be very reluctant to do is to use HSWA as a means of enforcing those Management Standards.
Further in the annual stats, one of the headlines is the amount of time lost by people off work for a number of reasons which collectively could be considered "stress". See e.g. Health and safety statistics 2024
So "0.8 million Workers suffering from work related stress, depression or anxiety (new or long-standing) in 2023/24" a number 60% higher than that for muscular skeletal disorders, so the bad backs and such like.
What HSE has NEVER done is make any attempt to publish a breakdown of what it thinks might be the causes of all this stress etc, so e.g. at immediate level:
(a) the stress that is work-related
(b) the stress that is NOT work-related
(c) the stress that comes from a mix of both
One result of this lack of any attempt to split up all the negative impact on human health is that organisations and OSH professionals consistently overestimate how much of this "stress" is work-related.
However, what they mostly don't do is then go about proactively manage the RISKS, perhaps partly as those are usually down to suboptimal management who don't relish being in the spotlight.
So, instead we get lots of sticking plaster measures to MITIGATE the harm ALREADY done. Mental Health First Aiders, Employee Assistance Programs (US spelling deliberate), bowls of fruit in break out areas and such like, but management don't sort out what is causing the work-related stress.
There is plenty that organisations could do to manage much of the stress that IS work-related and HSE could be looking for examples of poorly managed workplaces to enforce its Stress Management Standards.
"To RIDDOR or not to RIDDOR is not really the important question" (apologies to Shakespeare) as RIDDOR isn't about liability but simply a code of Regulations that are administrative in nature, designed to assist the regulator and thence the nation State to collate some information about levels of harm of defined severities and to provide some information about the causes of that harm.