Cant understand why you didnt pay to protect it as its so cheap TBH!
And its always "2 years less than our max discount" that they knock you down to as far as I aware, otherwise someone like myself with 20 years no claims could have prang after prang after prang and still be well over the max discount!
As mentioned already, although you will get 3 years discount still, you are also likely to get a loading applied to your policy due to the recent claim, so it could potentially double your policy between that and the loss of no claims.
Even with protected no claims they can still increase the initial premium due to an accident before they apply the discount.