I’ve read this a few times and it looks like you went out for the day and didn’t leave anything on your pitch, so to a new arrival it looked like it was vacant? If this is the case, then yes it’s your fault and as such is your responsibility to find another pitch! It’s clearly shown on the site info sheet and is not the wardens job to stand guard until you return! Hopefully you’ll be better prepared for more relaxing future stays on a pitch you originally  chose.

GC, Many thanks for your honest and impartial comments. 
I was actually the new arrival whom arrived at said “unoccupied “ pitch. I then connected electric and then went straight up to office to advise pitch number as I usually do whilst my wife made lunch. 
it was then that I found out that the pitch was actually occupied. It was then that head warden asked me to move as he didn’t want the pitch occupants to come back and have a confrontation with him. I asked what the protocol was in this case. 
I’m not sure he actually knew or there isn’t any in place. 
He eventually told me to stay on pitch but was not very happy about it. 
Anyway my wife and I didn’t want to upset  anyone, so moved and advised wardens. 
I feel that had there been protocol in place this could have been avoided.