Thank you for your reply Daniele.
If the UPC TV box is connected directly by ethernet cable to the UPC Connect box the settings in the diagnostics tab show as follows:
IPv4 address: 126.96.36.199/21
IPv4 Gateway: 188.8.131.52
DHCP server 1: 184.108.40.206
DNS server 2: 220.127.116.11
However, the UPC TV box functions fine when it is connected directly by ethernet cable to the UPC Connect box. This is not the problem.
The problem exists when I connect the UPC TV box to the LAN managed by the synology router. The diagnostics tab on the UPC TV Box is blank in this arrangement. In this arrangement the UPC TV box states that the ethernet cable is not connected (even though it is and functions fine in the other arrangement).
Please note that the UPC Connect box works fine as a bridge with the router and a range of different ethernet connected devices work fine within the LAN. It is only the UPC TV Box that has a problem. My guess is that the UPC Connect box sends a signal to the UPC TV Box that is different to the internet signal which its is sending to the LAN. Is that correct? Does the UPC TV Box require a specific port to be opened? By placing the UPC Connect Box in bridge mode have I not already forwarded or necessary ports to the synology router?