Help! Brake judder problem.

[Twinpipe]

A while ago I noticed a bit of judder coming through the steering under moderate braking.
I put some new pads on all around and then did a track day where it became infinitely worse, almost to the point of undrivable!
I changed the front discs and the judder went.
About a thousand miles in and it started to come back. (I'd driven to the Alps by this point)
Two thousand miles in and its getting worse again.
There is excessive dust build up on the front left wheel.
The car pulls left a little. (may not be related, haven't checked the geo)


My theory is that one of the pads is sticking a bit and causing the discs to over heat and warp.

Do discs warp that easily??

Would I get any judder just from a sticking pad??

Could it be a problem with the rubber brake hose?


I had a look at the calliper and all the pistons do move albeit one of the four is a little lazy.


Thanks for your input guys.