Ross, the information in my post came from today's Kent Live report headed "The 24 car parks and roads in Dover, Deal and Sandwich where Sunday charging could be introduced"
http://www.kentlive.news/news/kent-news/24-car-parks-roads-dover-1037207
which includes the following:
"Parking arrangements for St James will match other town centre car parks with the first half hour free – to enable a ‘click and collect’ regime – and a maximum four hour stay to meet the retail and leisure needs."
Although reading it again there is no specific mention that charges will be levied by DDC, it very much infers that that is the case. I was also under the impression that DDC owned the site but may be wrong on that point.