Hi khurramm

Your first posting here, so welcome to the Forums.

Lots of questions!

Your OTHM Level 6 Diploma (assuming in occupational H&S) meets the academic criterion for CertIOSH (formerly GradIOSH) and with your experience as an HSE professional in the field you should have the experience criterion as well to ask for an upgrade to CertIOSH if you haven't already done so.

Yes, you should have transferable skills to apply for jobs in the UK both in O&G but other sectors as well. 

Think about what the tasks that workers were faced with in your job in the Middle East whether you were working offshore and/or onshore, what the key risks associated with those tasks might have been and the methods adopted to mitigate the risks. Then think about how you can draw lessons from your experience to apply to comparable activities in other sectors.

You might need to consider what regulatory framework you were following either directly or as a guide when in the Middle East and perhaps do a gap analysis between what that required and what would apply in the UK - i.e. Health and Safety at Work etc Act 1974 and supporting legislation and all the other stuff that applies e.g. for environmental protection.

You probably do NOT need any particular additional qualifications at this time, but be prepared to consider sector specific qualifications either when you get a job or if you see a need to get something to improve your chances in any specific sector.