Give the FOS a phone call about this, as if you have complained and this is still unresolved after 8 weeks, the FOS can become involved and contact the Insurers on your behalf. The FOS process can take many months to resolve.
http://www.financial-ombudsman.org.uk/contact/index.html
The problem is that the Insurers would have asked at the time of taking out the policy, whether you owned the car, The V5 reg doc, whilst it does not confirm ownership, does confirm who the registered keeper is. If you think about this, how do the Insurers know whether you took out a policy for your brothers car and had not actually bought it from him. It could be seen as a way of obtaining Insurance for your brother, with you has the policyholder. Then when you had a claim, you would then say that you had not got around to sending the V5 to DVLA to be updated.
For this reason, I am not sure you should go down the small claims court route, as I think the judge may decide that you had entered into a contract on a false basis and have no proof that the cars ownership had transfered from your brother to yourself. If you have proof of the transfer, then you could try the small claims court route. If you do so, the FOS will then not get involved.