Had my car tracking done this weekend, and the little print out showed that the rear passenger side had a slight toe out, enough to take it out of what the machine classed as acceptable.

The rear is non adjustable so what can cause this? Can it only be down to the wheel bearings?

Car could have had a shunt, hit a kerb, worn bushes, and a few other reasons

No shunt, no kerb, will have a look into bushes.

Also, i believe these cars sit lower on that corner due to fuel tank, could affect the toe

Sometimes if new bushes are fitted the mechanic doesn't load the suspension correctly before tightening the bolts up.............copy from my post here

 

http://www.briskoda.net/forums/topic/165720-fabia-nut-and-bolt-tightening-torques/

 

Main pivot bush through bolt & nut = 45Nm (33lbf ft)+ 1/4 turn. Always renew nut. These should be done up so that they just touch the mounting bracket, then refit wheels etc. and lower car to ground. Open hatch and bounce car up and down from centre of hatch lower lip (this settles the bushes). Now you can fully tighten the bolts up (leave the car on ground!!)

Piston strut to beam bottom mounting bolt & nut = 40Nm (30lbf ft)+ 1/4 turn. Always renew nut. These should be done up so that they just touch the mounting bracket, then refit wheels etc. and lower car to ground. Open hatch and bounce car up and down from centre of hatch lower lip (this settles the bushes in piston mounting). Now you can fully tighten the bolts up (leave the car on ground!!)
 

Well ive had it checked at quik fit as it was worrying me, their hunter machine says rear end fine, but my tracking is still off, so i guess i will have to contact original garage and have a kind word.