Is the Asda car park still pay and display (refundable with purchase from the store)? That and the numbers may give them reason to move people on!
An alternative location, just in case, would be a great idea

and a good suggestion by Lucky

Not having been to Brighton in the evenings for a while, not sure what the parking issues are anymore..
I'm sure Baz will be on the case, as its showing some good figures for attendance
Guess the 'boyracers' are still under the arches in the evenings?