Could someone please advise me if it is a legal requirement to hold a permit to discharge into the atmosphere when using an incinerator, thank you

I work in an Energy from Waste plant. You are going to have to expand your question a bit more. What kind of incinerator is this?

In short, yes. The EA will be all over you, you are only allowed to emit so much emissions from stack and a lot of that emissions need to be neutralised before release possibly through flue gas treatment or other types.

What I have said is very loose and won't answer your question.