Thank you for all your comments.
After a lifetime of flying many types, I think I will continue to do as before, using bank upto 30 degrees on the circuit, or less, but not more, to produce the radius of turn required dependant on x wind, circuit pattern, etc., It has served me well for 55 years.
Of course 15 degrees of bank is appropriate at times. On the VC10 it was a company requirement to roll off bank to 15 degrees before flap retraction and IIRC the bank angle on the Boeing 737 was only 15 degrees following engine failure requiring an emergency turn, optimising climb rate on one.
I was flying a Warrior which climbed perfectly well ( 2 up 2/3rds fuel, 22 deg, c. ) at 30 degrees of bank and I absolutely believe that any and all competent pilots should be able to easily manage flap operation in a turn., the risk of asymmetric flap being extremely remote. Perhaps I am wrong in believing that a light single will have enough roll authority to overcome asymmetric flap, just as the 757/767 could handle asymmetric leading edge extension.
Someone mentioned Bomber Command circuits, reckon I could have done a tighter visual circuit in a Canberra than some of the lumbering circuits I have seen on some single pistons !
I will discuss the issue with the CFI and try to get to the root of the issue.
Thank you , again, for your comments.