Hello Peter,
Further to your question about the decoder in the Hornby Class 101, I have found that with my Hornby motored ex Lima models (Class 59, Class 101, Class 121) it is those pesky Feedback Parameters that need tweaking to obtain a smooth response from the motor.
CV 53 was lowered slightly to a value of 50, CV 54 to 20, and CV 55 was bumped right up to a value of 55 to emulate a large flywheel. These numbers could obviously be improved upon with a little trial and error as not all motors will respond the same.
By the way, I love your railway, I have just been selling off all my current era models to go back to my beloved BR Blue period, just waiting for Hornbys much delayed blue and yellow HST pack!
Geoff.