Dont bother with the certificate, do the diploma straight off. I think rapid results college do it correspondance and use your ELC to pay for it unless your looking to do it as resettlement. The diploma can be done in 12-18 months. You will need at least the diploma for a decent job in civvie street. see link
You will get a job with just the certificate, usually if you have experience and never a very good job. Have a look at SHP Online jobs section. A lot of employers ask for IOSH membership which you need at least the diploma for. And as far as the British Safety Council Cert/Dip. Not worth the paper they are written on to most employers.
If you have a bit of time left, much better to do the diploma and then use the remainder of your ELC to go post grad route. Portsmouth Uni runs good PgC or MSc courses which you will get on with the NEBOSH Dip. I did the PgC there and it wasn't difficult, again correspondance. Once you have the NEBOSH Dip, if you apply for membership of IOSH, you can use the post grad study as CPD towards full membership.