When I'm on 4 wheels I NEVER pull out on a Biker however close they are, but I think you will find that the car driver admitted he never "saw" the bike or car behind it, in other words he didn't look or it didn't register.
I commute 10 hours a week either around or through Bath, as for your comment on being a sitting duck then you are right, you have to ride defensively or you won't last long. Think of it as a big game of Russian Roulette, one or more of the drivers is going to do something stupid - you just have to guess which one it is and when....
You can do your best by taking every precaution and riding safe - doesn't have to be slow - just safe.