Well regardless of what appeals to you, maybe you should ask yourself the reason for this change?
Many believe this is an easy field of work and something that can be achieved quite easily as a secondary career. I think this was the case some years ago however, this is less so these days.

Many health and safety professionals go through much higher academic courses via universities than ever before. But the General Cert is a good start still for many.
As you already work in construction related role maybe you should concentrate on that. I would certainly look at the Construction Cert once you have completed the General Cert.

One of the issues you may have is pay, you will need to address this realistically! A secondary issue that is abundant at the moment is unemployment. The recession has hit the health and safety industry hard and you may find yourself competing for roles with practitioners who are highly experienced and qualified to the hilt.

You should ask employers you know in the industry and seek their opinion in relation to obtaining your first role. You may be able to take a part-time role on top of your current job function?

I hope this has been some help and wish you every success.