We're having the same issue. Kept getting back on the phone to Sky. First sent out a router as a guess (yes really..) and of course the issue persisted today so rang back and an hour later after actual tests they've determined a faulty ethernet cable and are sending out a new one. We shall see if that works.
My advice is simply keep calling Sky. Eventually they'll do the tests and figure it out hopefully.
Even though our issue sounds identical; keeps dropping on and off. The cause could be an untold number of things and honestly the only people with the tools and diagnostics available at their disposal is Sky themselves so you have to call and play a little bit of "pass the parcel/customer" until they figure it out. Stay calm, ask that they do tests, have patience.
Prim.
