I posted this a while back but you might find it answers some of your questions:
A few notes on 'how to':
First - to be a commercial diver in the UK you have no choice but to be an HSE Approved diver. This means an HSE Approved Commercial diver course. However you can economise on this if you are ex-military diver by undergoing an Experience and Comptetence Assessment at one of the HSE Approved schools (I'd go for the new one
www.professionaldivingacademy.com).
Second - look at the IMCA website for guides to careers - this is the International Marine Contractors Association which is the trade body for all the major diving compamies arounfd the world
www.imca-int.com
Third - surprisingly times are good to get a job after your course due to diver shortage in the Gulf of Mexico following the Hurricanes and the price of oil making every oil co. in the world desperate to get it out of the ground - the same cannot be said for diver rates which are still 'mixed' - especially if you get a non-UK job as a 'baby' diver. They will take advantage of you as you are desperate to prove yourself and need the experience for your cv.
Fourth - look a the
www.longstreath.com website as a good indication of the wonderful people you may end up working with....if you don't like what you see stay at home.
Fifth - if anyone tells you you will earn £1000 per day they are not quite all there.... some jobs do pay well but it will take you years to get the. If you are prepared to hang in you are one of the few.
Six - if you are just doing it for the money - become a plumber.