Premium pitch / pup tent

Hello all,

We are staying on a premium pitch at West Ayton. We put up a small pup tent on the pitch and told by a warden this evening we have to move it onto the gravel or take it down. the tent isn’t suitable for gravel, it’s a small trekking tent  

We paid for extra for the space so we could put up a small tent. The pitch has a BBQ stand and space for a table (there is no table) The pitches are separated by beech hedges. I don’t understand what the problem is if we put up a pup tent on the grass on the confines of our pitch. We haven’t put the awning up. The grass pitches are still open and awnings are allowed on them. 
I have read the rules, I can’t see what the problem is.