Bad luck mate.
The reality is, in this day and age, the Police/CPS will not generally prosecute for due care and attention, unless there is a serious injury or serious breach of Road Traffic Regulations. The public interest is not served if either do not apply. Also, insurance companies look to initially deny liability, then negotiate and mitigate to reduce liability to end up paying as little as possible. You have done the right thing to secure evidence of the incident (photos), but the account of any witnesses may also go for/against you (eg speed/driving style/traffic flow etc). Given that you were complying with the Highway Code (not law, but accepted doctrine) you are in a good position to get a positive outcome. Approaching a roundabout to turn right should be done in the offside lane.
Stick with it.
Cass