I've had to lock it in, rates are only going up, and this is the only provider we can go with as there is no credit-checking as existing customers, I doubt any other lender would touch us, and looking at the rates, they aren't really any different elsewhereYou can if you apply via a broker to a different mortgage company afaik.
Also potentially consider tracker, not financial advice but if rates come down you'll pay less later, or not be locked in on a higher rate. Depends on your risk for appetitie.