After spending the equivalent of several days scratching my head, looking at datasheets, unsoldering parts, replacing parts, re-soldering parts and just generally despairing, I have finally worked out what was wrong and the dual motor driver for my SuperRobot is now functional. I had been moving from a plug in wired protoboard solution to a soldered Veroboard construction, to achieve a greater reliability, testing the system as I moved each set of wires. I had transferred the wires for driving one DC motor which then would not work. I eventually worked out after great angst, that I had connected the signals for driving channel 1 but had connected the test motor to channel 2. Obviously that doesn't work. So not an actual fault, but it still didn't work.
I have now fixed this fault, which wasn't actually a fault at all, just me being a bit dim, and I am able to control the SuperRobot motors. My next step is to connect both the DC motors securely with soldered wires and check it still works. I hope it does as I am running out of enthusiasm for soldering things together as well as time to make some more progress. I might have to amend my original idea for SuperRobot to something achievable in the remaining time.