Hello pal,
The best way is through the Nebosh route. I done mine about 2 yrs ago. I bought a disc off ebay, then studied it at home then just booked the exams which only cost me about 300 quid in all. You need to do the nebosh general cert 1st then you go on and do the construction, fire or enviromental if you want.
To be fair though I was a HSE man with cape on sellafield and it bored me shitless, it can be really really ******** at times especially when the majority of management have never turned a spanner in their life. You have to be prepared to drop the lads in it as well which I couldnt bring my self to do.
Its a queer road to go down mate, I`ve gone down the supervisors road now which is a hell of a lot better.