A few years ago, we went to renew our longstanding home ins. policy with RSA and were told that because we'd had several claims over the previous five years (I think it was 4) they couldn't renew.
I then contacted every other insurer who declined to take us on. I was getting desperate when the last company I spoke to informed me that RSA were legally obliged to renew our policy - albeit at a higher premium.
So back I went to RSA, told them I believed they were obliged to renew, and they said...er..yes, that's right. They barely loaded the premium at all - after all that!
Now I realise that your case is different, but refusing your business on the basis of one single claim (when you already have another policy with them) seems extraordinary. I always dealt directly with RSA, never through a broker. Do you think it's worth while ringing them up and appealing to their better nature?
Oh, and I've just moved from RSA to AXA (who already insures our 2 cars) because they were way cheaper. Have you tried them?