A 'middling' claim is one that isn't enormous but isnt trivial. One that with admin costs would represent more than a couple of years premiums and make the insurerst think about how to get the money back!
If you don't declare factors that you are required to or if you tell lies then the insurers may refuse to pay out a claim and leave you in the lurch. Franly I don't have much sympathy for people who misrepresent the risk, they make it more expensive for me.
Sure thay have not asked but if you read the small print you will find that you should inform them of anything and everything . . . Not just a claim on another policy but even things like a pending prosecution, fitting wider wheels, sticking a bullbar or winch on the front of a 4x4 or allowing the second or subsequent drivers to do more frequent driving than the 'first driver'. (That's one that really gets me as irresponsible and inexperienced drivers often spend several hours per day on the road on a policy that partner, mum or granddad took out for a couple of hundred pounds. When they have a claim for a couple of million guess who is footing the bill?)
Like BB says, you must report things, the onus is on you to ask if they want the information - and I suggest you always do that in writing in case they say they don't want it then later say you had hidden it from them and they will quibble about paying out a claim.
KRs Funforus