Tech support, after having me unplug everything in the house, as well as switch the kettle off, have admitted their servers are maxed out
Get a decent ISP. It has been this way for many years. So-called 'maxing out' means that they cannot deliver what you expect. Look at the PC World awards or broadband fora for recommendations - and make sure they deliver in your area. I have nothing to do with the people I am with (they just get my custom) and will not advertise, save to let your karma guide you.
BOFH