Hello Nigel, welcome aboard! [:)]
I have P21/8 so our boats should be similar. Apparantly Bill Parker was still developing the P21 in these early stages so I still expect some differences. I bought my boat at the end of last season and am still trying the get ready for this season, I am changing the foredeck hardware, adding a bow roller, sealing and adding an anchor locker drain. #8 was returned to Parkers for the multiblock winch to be fitted.
Looking in the P21 Technical Handbook which I have a copy of, there is mention of a wire strop fitted to the top of the keel, this should in turn to connected to a shock cord attached to the mast to indicate the position of the keel.
By the way have you found an anode anywhere?
Alan Needham P21/8