Are all sites fully booked at weekends?

Hi, wanting to go for a weekend away as soon as poss to try out the new van, but I am amazed that all the CC sites I wanted to try seem to be booked up already.. If it is like this in March, are there ever any vacancies in the summer?! I am trawling through CL's now for a pitch on  a quiet site within walking distance of a /town or visitor attraction in Derbyshire, Lincs or Yorks, if anyone has any suggestions!