2010 1.4 titanium 

had alignment done twice swapped wheels around and changed bottom arms but car still pulls left all the time has anyone got any ideas what this could be 

Brake caliper slightly binding. It only has to be holding a very small amount to cause a pull to one side.

Other guys probably know better, but what about track rod end(s), excess play in the steering rack, these 2 can be given more insight by jacking the car up and see if there is any play when moving the wheels (either side) from top to bottom and left to right, just like they do in the MoT, or the anti roll bar (most noticeable when hitting bumps in the road), I had that many years back, almost threw the car off the road when it hit a big pothole, but in my case you could see the gap between the rubber and the bar looking along the bar, needless to say there shouldn't be any gap at all, also look at the suspension, is the shock losing oil, is the coil spring broke or fractured, all these things could cause steering to play up, gives food for thought until any more certain answers come in.