https://www.nebosh.org.uk/qualifications/environmental-diploma/ 

1) There are no formal entry requirements for this qualification. Achievement of the NEBOSH Certificate in Environmental Management or direct equivalent prior to undertaking the Environmental Diploma course is highly recommended.

2) & 6) search function on these forums (top left under membership tab)

The qualification focuses on the main elements of UK and EC legislation for environmental protection and general principles of the management of environmental and pollution control.

Answers 3) - No, 4) - No, 5) - No.

Hi again Karan.  The following is based on my knowledge of IEMA's offer in this area; I know little about the NEBOSH versions.

If a CSR element is desirable, you might look at the IEMA Certificate as an alternative.  For that it is recommended to do the IEMA Foundation Certificate first which also goes into the principles of sustainability (going beyond traditional environmental protection issues to include socio-economic issues).  The full-blown Certificate is quite a major undertaking but the Foundation Certificate is relatively quick, easy and cheap to do.