Clearly not something anyone else suffers or has noticed!
Just to update this thread for others, the tool shop sent me out another unit and this suffers the same issue. Spoke to dewalt uk and they felt it was not correct and the saw would need to go to a local service centre for inspection.
Sadly this is some distance from me but I gave them a bell and spoke to their head technician who commented that due to the design they need a small amount of play but this sounded incorrect. He told me of a manufacturer adjustment screw for the slider bush in the saw body which I adjusted and could make some difference but sadly not an amount that I feel is acceptable. I found this same adjustment screw on my ancient elu and frankly this now has less waggle than the new one!.. I think I will invest some time in this old saw (20yrs + young!) and give it a good service and whetstone the base.
All that said, I’m sure that this DWS777 would still be a good saw for 1st fix and most 2nd fix applications , the issue will rear itself on bevel cuts most prominently. Perhaps I just expected too much from that budget and am used to the accuracy of my festool saws - which clearly cost double.....