My mk4 drives, accelerates and brakes in a straight line on a flat, smooth road (wherever they are, lol). If I drive over say a pothole it'll tend to pull left. Even worse, when the road surface is bad, like when they've surface dressed it years ago and its now broken up, the car will track left and I need to deliberately steer it straight.

I had a mechanic look at it, they didn't find anything at the front of the car, but mentioned both trailing arm bushes had some slight wear, I should look at renewing them at some point.

Could the dodgy trailing arm bushes be the cause of the car tracking lift on rough road surfaces?

I'd check inside of tyre for uneven  wear can happen and rest of tyre looks good , probably have a worn shock if it's there , I'd also change the droplinks , easy and cheap and could solve it 

Try switching that front left tyre for the rear, could be a tyre pull.

Thanks, I'll give those a look. I'm suspecting the shock absorber now, I went over a speedbump a bit heavily earlier and it felt like there was little rebound damping