Wagtendonk is by far your best bet. As for a past papers, forget it! Ask your school if they have any; the school I went devised a few for each subject. The same goes for Flight planning and performance. It IS helicopter specific (as we don't have runways) so you can't use The Confuser.
I believe there is a Q&A book published by AirLife written by Dorothy Pooley (or whatever her name before she married) that has a helicopter section. There are also some Key Facts and Key Q&A which are helicopter based. These are aimed at CPL students but the standard isn't much different.
FP&P is a "catch-all" subject covering all aspects of flying not otherwise covered in any of the other papers. It is mainly common sense and much of it you will learn from your instructor. I did no work for it and winged it on the day with 78%.
Cheers
Whirls
Teeny word of advice. This forum is rarely inhabited by helicopter people so Rotorheads is always a better place to ask!!