unplug wheel sensor = zero miles?
Lol i can guarantee it's much more advanced than that!
For a start if it's not regularly synced, then the company will probably be phoning you to ask why its unplugged (plus there's almost certainly a clause in the T&C's that you keep it plugged in).
Also it'll no doubt log the total mileage, so it's hardly like you can unplug it before using it on a long journey, because as soon as you plug in back in, it'll notice an irregularity in clocked mileage, and then the insurance company will be back on your case + likely resulting in insurance being cancelled.
My GF only does about 3k miles a year in her car (infact i probably clock most of that), so a quote for hers is £190 base, and 4.3p/mile. Which works out about £320 a year. Even if we clock an extra 1-1.5k miles the total price is still at a max of £380. I think she pays maybe £400-450.