you get hit from behind, its the car behind youse fault.
as happened to me - a car hit me in the back - pushed me uphill into the car in front. I still had to be the guilty party in his (the car in front) claim. - even at the time I was sitting , with my engine turned off and the handbrake on.
so if the car in front stops for whatever reason , its your fault if you hit him.
It doesn,t matter cyclist or another car, if they make you swerve,brake ect and you don't hit them but hit another car, they are not part of the accident. you are very unlikely to be able to claim against them.
Its the classic "I'm a good driver , I see loads of accidents in my rear view mirror though"
If the bike actually hits your car then you can chase them and get thier details - as happened to a friend of mine, but the insurance companies are not interested as they aren,t insurered and its not worth going through the courts to get the money. - its just your no-claims that gets nailed.