"only thing that has changed is a new fuse box put in to power a new cooker and cooker hood in my kitchen. Could that be causing it? And if so what can be done about it?"
Process of elimination of any and all electrical equipment, You can check if that is the cause by switching off trip switch for that circuit/radial in your fuse box, and see if it solves the problem.
In fact if you switch all of the trip switches off - just leaving the ones you need to power electric plugs circuit for modem, router and pc - (and also disconnect any other equipment tvs, radios etc) then switch on each in turn (trip switches and other equipment) to see if any affect the Broadband signal (interference starts again).