I do not have the TV package, only broadband and landline. The tV signal is therefore via a standard domestic roof mounted aerial.
When using any wifi device in the lounge where the router is - especially in the evening - the TV picture is very badly affected. I would add, the router is next to the TV where the engineer installed it. It's just a bog standard flat screen.
Standard advice is not to install a hub/router close to other electrical equipment, especially a TV, for the very reason you have discovered. Unless you specifically asked the engineer to put it where it is, then he has messed up.