I had a similar situation with home/buildings insurance about 20 years ago. I made a claim for a new garage door after a break-in. Subsequently, I changed insurers and the new insurer did not ask me if I had made any claims. A couple of years later had to make a claim with the new insurer for replacing a sewer pipe because of tree-root damage. I remember receiving a phone call one morning from the insurer telling me that I had failed to declare the claim from a couple of years earlier and that they could not settle the new claim until my premium was adjusted. If I recall correctly, the additional premium was about £30-40 so I just paid it.
Looking back, I am fairly certain that the insurer was on shaky ground. Why else would they offer simply to accept a payment that reflected the difference in historical premium? I could have argued it, but it wasn't worth the time and energy.
