Who's at fault?

I was wondering if any one knew legally who would be at fault in the following situation.

I was pulling out from a junction on to a dual carriageway (40mph limit). I waited until there was a gap and pulled out. I was half way into the left hand lane when a car in the outside lane decided to switch from the outside lane, into the lane I was now partially occupying without indicating. The back passenger side of his car hit the front drivers side of mine.

In my rose tinted view I'm quite adamant that I wasn't in the wrong and there was nothing I could have done apart from wait until both lanes of traffic were clear just in case someone wanted to switch lanes without notice (which, at rush hour, I'd have been there for about 3 hours). I have a dash cam which shows me quite clearly stopping and waiting for a gap in the inside lane to pull into, getting halfway into the lane before i'm clipped as he comes across me without indicating. But would his insurers see it that way? Is there an argument that he can switch lanes? Even without indicating? Or should he be aware that I was pulling out of the junction?

Any thoughts or opinions would be a great help. If The Highway Code backs me in away way that anyone knows about, it could mean the difference between going through my insurance or just trying to settle with him.

Thanks