BS5306-8 is overkill now and as for litigation some of the clauses wouldn't stand up in court under expert witness scrutiny.
This isn't the days of the prescriptive FOC rules (which were criticised even as far back as '61 in the FBU practical guide for fire officers enforcing the 'new' Factories Act fire certificates) it's risk assessment.
Most of the time you would be following most of the contents anyway, it's some of the more questionable and inflexible clauses that, in specific cases, can be deviated from or interpreted more differently.
It's not in an extinguisher engineers interest to reduce the number of extinguishers on a site and as for risk assessment they need to be careful they are competent - some are (& can do full FRAs), some cannot (and end up in jail). And considering all the negative feedback I hear on some providers technician courses they can't even refill an extinguisher let alone start risk assessing.