It is normally worth phoning for PPR in advance although nice just to drop in too (brings in landing fees/ sells fuel/ life blood of an airport etc).
The joining procedures (Fixed and Rotary) are not so complex that a PPL cannot handle them without prior briefing (its on the outside of a City (right on the City limits in fact) and there is no restricted area around, so actually easier than Denham/ Fairoaks/ Blackpool/ Leeds Heli/ Sydney Bankstown/ etc.
This is of course what flight guides and approach plates are for.
The reason may lie in the assumptions about liabilities of the airport in the event of damage ?? (see AOPA December magazine).
I don't want to say anymore in an open forum as one of the resident pilots has just had notice to quit served for being 'difficult' in writing (reported in local paper so public info).
PM is you want more.