The moorings at the park in Reading are chargeable in theory, but, as the owner of the boat cafe told me last year, he incidentally moors just above the bridge on the other side and has done for years for nothing, are an illegal charge because they cannot issue you a receipt!
Also, there is nobody to collect these fees, or wasn't last year!
While I stayed there for two days, someone actually phoned up the number on the sign post and was kept waiting for 10 minutes while the office desperately tried to fined the book to enter his fee!
He then asked where he could collect his reciept and was told that they didnt issue any!
Needless to say, he didnt pay and stayed there his two days without anyone trying to grab money!
I will add that this only applies to the Reading moorings including Tesco's as others are run by agencies who have the right and will pursue you for fees as large as £200.
Having said that, don't be put off by these signs as there are loads of alternative moorings on the Thames, but be prepares to tie to a tree!
Nipper