Sounds as if you are both responsible- a cyclist should be aware that a car may turn into a turning ahead, you definately need to keep your wits about you on two wheels and be aware that you are hard to see, and you should not have responded to a flashed headlight.....flashing the lights means only one thing to the law, its a warning, which means 'look out, I'm here'...it doesn't mean 'thank you' or 'please turn before me'.
It's meaning is ignored in this country and it's a shame, as if you're on a motorcycle it's often your only means of warning that you are there, but abroad they DO flash their lamps as a warning.....and Brits often get in accidents with the locals as they think it means go ahead.....
Check the highway code-for you, rule 90 & 91, for the cyclist,
rule 57-59.
http://www.highwaycode.gov.uk/index.htm