Is a written spill plan overkill for a small yard in Al Quoz?

We keep about eight IBCs of various chemicals in our yard in Al Quoz and a client’s HSE guy asked to see our spill plan, which was awkward because we don’t really have one beyond “get the kit and clean it up”. He made it sound like rigorous chemical spill planning, Al Quoz style, was essential, but I’m not sure if he was being thorough or just covering himself. What does a spill plan actually need to contain for a setup our size? Do I need a formal document with roles and procedures or is a laminated sheet by the spill kit enough? And has anyone actually been asked to produce one during an inspection, or is it one of those things that only matters on paper?