I work for the EA and was an Environment officer for 5 years.
EO job interview are likely to be capability based, e.g. "Can think of a time when you've ..."
Best advice would be to try think of example for stuff within the job spec / advert. Influencing skills, dealing with hostile situations etc. your examples won't have to be the Oscar worthy but should demonstrate you meeting the capibility. Kinda like the STAR model the fire service use (or did when I applied!)
Knowing some legislation details would be in your favour but you won't be expected to know it all!
Remember to answer the question, the whole question and nothing but the question! You'd be amazed how people go off point trying to sell themselves and don't answer the question!
Hopefully that helps if you want anymore advise message me email in profile