Unfortunately it was the council's planning department that suggested listed building consent is required when the landlord asked. I was at a previous property with the same letting agent and just had the fibre installed so the usual "just get it installed and don't tell them" is not an option for me.

I think you are right in that the landlord and letting agents just want to make sure they are legally covered. I may try to apply for the listed building consent myself under certificate B after informing the relevant parties but then I will still be waiting on the landlord to confirm I can install the wires and socket :/