It would appear that the SIM900 shield I had attached was switched over to UART mode.
When I disconnected all the shields and started from the UNO, all uploaded.
I kept adding shields and uploading until I added the SIM900 shield, then it croaked.
Luckily my first kludge was to flick the UART switch and try again. Voila 1 UNO uploading very happily.
Moral of the story RTFM
Thanks and kind regards,
jB 8)