Dude, I hope you have good insurance! Might be a bit tricky explaining to the CAA why you were operating outside the manufacturer's recommended operation and outside of the operating handbook.
If I was you I would be scanning my insurance very thoroughly as there is usually a clause in there about operations outside of the norm.
If you want to find out more why not get in touch with either Piper or their UK agent and ask them about it? If you could get something in writing from them saying its OK then at least you'd be covering your ar*.
By the way, I have a few hundred hours on Pipers and I have yet to find an airfield where either no flap or flap 25 didn't work.