Bazile has hit the nail on the head.
It is part of your insurance terms and conditions that you MUST report all accidents, regardless of fault, or whether you wish to claim.
As noted, insurance is based on the likliehood of an event happening, and if you don't report a claim (even if you paid for the damages yourself), but you then inadvertently tell them, say due to having another claim, then it can cost you.
It is a strange system (car insurance now), that even if you have an accident that isn't your fault, and we recover all the money from the person at fault and allow your NCB, that your premium still goes up.
This is because some number cruncher got statistics stating that someone involved in a non-fault accident is more likely to be at fault for their next accident (can't say I've actually seen this happening myself, and I've been doing this for a while).
I suppose that with household insurance, there is a limited number of circumstances/incident that they deal with, and it probably makes more of a difference to their pricing arrangements, but don't quote me on that!