grass at Wigram, where I was not to touch the brakes, but taxi using only the tailwheel lock and power
That is a complete no-no as the strain on the tail-wheel locking system is significant. The tail wheel lock was specifically designed for the take off and landing run where in theory the aircraft runs straight. Being taught not to touch the brakes amazes me How do you pull up otherwise? - if you are taxiing using differential power and tail wheel lock all you are going to do besides eventually stuffing the tail wheel lock is to pick up more speed!
