We visited the new centre and pontoons at Portsmouth last Friday.
Unfortunately they were expecting a number of boats and could therefore only find a place for us on the outer pontoons. These pontoons were very high for my little 18footer - Not possible to tie up with the wash thereabouts without damage.
Apparently if you are visiting you go to the centre manager's office upon arrival. This office is located a couple of hundred yards up the road but we didn't get that far.