A lot (the majority?) of household policies have ncb's these days (typically 30%), that way they can quote you a low excess and then claw their money back on next years' bill should you make a claim, if you try elsewhere, surprise surprise, the new company know all about your claim history and quote you accordingly.
Think carefully before making a claim but if you do go ahead make sure you screw them because they are certainly gonna screw you back, you can be sure of that.