That's what I did.
So to check the cable, tried connecting it direct into the laptop & with DHCP could (just, v faint) see its new ip address & that was connectable OK.
Tried again with the cable into the router and after some re-booting it now works.
It had reported network connected, but maybe reboot was needed to make it work. Was complicated by not having long enough cables - either connect to router or to TV but not both, so couldnt see what ip address was assigned! Now have longer cable & can do both.
Thanks for the input