Hi Ben
Perhaps you are one of the many who don't do well in an exam room. If so NEBOSH might not be the best development route for you.
I don't think you would have much chance of any role as a health and safety professional without a basic understanding of legal requirements but in practice the law is not that complex and, if anything, it has become simpler over the years.
These days almost all statutorty requirements are governed by the qualification that AK has mentioned - to do what is "reasonably practicable" - and to be honest, you don't even need to know the detail of the legal judgments as this terminology is very rarely tested in the Courts.
To put this into nerdish perspective there are two "authoritative" judgments on the meaning of "reasonable practicability" - the usually quoted Edwards v NCB and the less familiar Marshall v Gotham, which sets a somewhat less stringent standard - that judgment clarified Edwards v NCB, 5 years later, and in a higher court, so should be the gold standard, but is usually ignored, even by the Health and Safety Executive!!
Usually when something has gone wrong it is obvious whether something was or was not reasonably practicable (usually it's about working out what is done in comparable scenarios), so nobody ever ends up distinguishing between Edwards and NCB v Marshall v Gotham - I did that in detail ONCE in 40 years on a very specialist project.
So in general you wouldn't need to know which requirements are "absolute" or "strict liability" duties, from time to time you might need to understand that a requirement is qualified by "practicable" - without the "reasonably", but on the ground that "reasonably" tends to be reinserted [perhaps without realisation] purely for pragmatic reasons of what can practically be done to reduce risks.
In very simple terms doing what is reasonably practicable is about balancing the risks against the costs of mitigating them, to find a proportionate solution.
In making that balance you need to consider "time, money and effort" and any new risks that precautions might introduce.
An example I often use to illustrate this is minor work on my own home roof. I live at the top of a Victorian townhouse with basement and four storeys above, so it is a very long way to fall.
There is permanent access from a dormer window on to a narrow flat roof at the front of the building. That enables access onto a very steep slope, then a less steep slope to the ridge and similar on the rear, except for the flat roof (and no rear dormer).
So, imagine a job on the lower rear slope that is going to take 30 minutes to complete.
The immediately obvious solution is to build a scaffold at the rear to provide access direct from basement well and to provide protection from falling from the edge of that lower slope.
But this means erecting (and dismantling) a scaffold about 18m (60 feet) high. Even with best scaffolding practice, this means putting scaffolders at significant risk + there is the heritage cost (very difficult to put ££ against) of the need to drill holes into a Listed Building to "tie" the scaffold to the building.
HSE guidance tells me that it is probably not reasonably practicable to erect a scaffold to prevent someone falling from the roof - even without considering the risk introduced by applying such precaution.
So, the pragmatic solution is to have highly experienced slaters using ropes to get up and over the ridge and to stop them falling from either front or rear of the building.
That's the legal explanation, now for an alternative to NEBOSH....
If you have a supportive employer you could do a (National or other) Vocational Qualification with the key milestones being at whatever is the equivalent of European Qualifications Framework (EQF) Levels 3 and 6, noting that NVQs and e.g. SVQs (in Scotland) do not align the same way against EQF.
Doing this is about putting together a portfolio to show your understanding of various principles of managing health and safety - including the legal bit! But, you could use your day to day work and the paperwork that results to build most of that portfolio.
So, you are faced with a problem - you assess the risks and you come up with various options to mitigate those risks - you discount some options as not being proportionate (i.e. you don't think they are reasonably practicable) and you select one or more precautions that are appropriate.
Thus you show that you understand the legal principles by putting them into practice at the coal face, rather than in an exam.
Another option would be NCRQ - this is two Level 3 Certificates followed by an assignment to complete a Level 6 Diploma away from work.
You are presented with various assignments to test your understanding of the principles (including the legal bit!). You can't do this at work, but this does mean that you are not in danger of simply accepting custom and practice at your work as being acceptable, but that doesn't mean that what you have learned in your work has not given you transferable skills, knowledge and experience which would help you think through the issues in the assignments you are given.
With a Level 3 qualification under your belt, opportunities should open up. Get Level 6, more opportunties.
Good luck, Peter