This is clearly UK but here's a few fun facts for Americans to chew on... California is the only state in the USA where lane splitting is legal. In total motorcycle accidents per capita, it is one of the top 6. But as for fatalities per capita, it comes in at 22nd (2017 NHTSA). When you look at specific data like deaths per capita for all motor vehicles and deaths per million miles for all states drivers, California becomes pretty average.

Which means that, you can't realistically say lane splitting increases the risk of accidents. But you can realistically say lane splitting decreases commuter time (time but not congestion).