Agree with never auto renew with current provider.
Historically, my renewal is always more expensive than the previous year even though there has been no changes.
I always go on the various price comparison websites (confused, compare the market, gocomapre etc) as even they give different answers.
Sometimes, its even my current provider which is the cheapest but their renewal isn't (if you know what I mean), but regardless whether they are the cheapest or not, I would ring them and tell them I've found cheaper and ask them to match or better it and they would usually do in which case I stay.