Resolved:
After unboxing the second new WD drive it worked fine. Swapping the cable to the first drive and it then worked as well. I was reluctant to unbox the second drive at first due to potential return issues.
If having USB 3 issues always try an alternate cable.
Dell offering to replace the motherboard and then sending me a replacement laptop due to a “suspected motherboard issue” was very generous but given that everything tested ok a rather expensive way to check things. The new machine was returned and the WD drive exchanged at my local retailer with no questions asked.
Thanks to those who responded.
