IMO Chartered stautus will do more for your career prospects that an MSc. I have a PGDip but people are only ever intersted in my CMIOSH status.

Spend the money on specialised courses and get relevant experience IMO.

You can also use your NEBOSH quals as accreditation of prior learning, meaning you don't have to complete certain modules. It's worth talking to the individual providers about it.

You may want to get some clarification regarding IPD and MSc projects/dissertation/thesis. It may be possible that depending upon an MSc project/dissertation/thesis specification, it could count towrds IPD. An MSc certificate is no basis for counting towards IPD, but it may be possible to structure an MSc project/dissertation/thesis around the IPD requirements--not a simple or easy thing to dop.

Regarding employment prospects, having higher qualifications could be an advantage for senior positions in some sectors of industry, even if you are already Chartered Safety and Health Practitioner (CMIOSH). This is because the Masters courses include greater depth and breadth of learning, including practical applications by means of assignments etc.

It really depends upon individual circumstances and your industry sector--for example, it is likely to be an advantage for senior positions in phamaceutical/high value chemicals/other high technology sectors where it is valued,(because the overall level of education is much higher in those sectors) in comparision to other sectors such as construction, public services, facilities management

I am currently undertaking an MSc in Health, Safety and Environemental Management and have been informed by IOSH that it does not count towards IPD, although it used to.

Have to say that although it is a hard slog and it takes up an incredible amount of my own time, it has, on reflection, been enjoyable and very educational. It has changed the way I conduct myself and the how I assess issues.

You should be able to gain chartered membership with the NEBOSH Diploma and relevant evidence so there's no need to spend money on specialist courses for CMIOSH. CMIOSH is probably of more interest to prospective employers if you stay in the health and safety field, however, MSc is probably more recognisable to people outwith the industry so may be of advantage in consultancy where the client is not familiar with NEBOSH. Really depends where you wish to find your clients which whether it would be an advantage to have the MSc accolade after your name.

Hope this is useful.