What a bummer .. and unfortunately I think you may have problems proving your case ..

I was involved in a lane change roundabout accident 5 years ago, the other guy simply cut me up, no signals and changed lanes for no reason, I had no chance to avoid him.
The insurance company told me quite specifically that as it was extremely difficult to prove "blame" given no witnesses, it was my word against his and "knock-for-knock" was a reasonable decision.
Further, this was their policy on rounadabout accidents.
I argued strongly, including many photo's of the approach roads, signs, road markings etc but was getting nowhere. They eventually sent me his version of the events at which point I was able to make a very strong stand. He had claimed to be in the middle lane as he entered the roundabout. The photo's showed there were 4 lanes and I was able to ask how he could claim the "middle" lane of four lanes, and make further inroads into his arguments.
His insurers then accepted liability and I got all my costs and no-claims back...... but it took over 6 months ...
