Thanks for the response from bed - above and beyond the call of duty! 
Just fired it up again and see now I missed the very nice status display below the main 3D window when a job is running showing gcode line, % completion and yes - option to speed or slow feed rates in real time. And all that disappears if no job running.
Think I was concentrating too closely on the CNC first couple of times with one hand on the GRBL reset button and other on main power - wasn’t relaxed enough to be watching what gsender was doing.
Thanks again,
Rob