@Old-timer,

If you have an ethernet cable plugged into the TV, there is no need to connect to Deco's wireless network. The Sony TV should detect the presence of an ethernet cable and automatically configure itself to work on the connection. If you are able to stream Netflix and Amazon Prime, that means that your TV is connected to the Internet and that there would have to be another reason that you cant view BBC or ITV.  As these are non-US services, is there a chance they are region locked?

  @Old-timer,

If you have the Ethernet cable attached to the TV while you are trying to connect the TV to a Wi-Fi network, it may be providing that as a generic error, as the TV is already being supplied with a hardwired connection to the internet.

When you are in the network settings for your TV, does it list the Ethernet as being connected? If it is connected, there may be a speed and connection quality listed.

Otherwise, you may be watching Prime Video or Netflix on a Streaming Device Connected to the TV.

I know that in the case of ITV Hub, you are required to have an IP address originating from Britain. This may very well be the case with BBC Player. If I am correct, in the US we have a separate BBC application for paid subs and then BBC America. You will have to look into VPN options to see if a VPN would work for your situation.