I have just been told by Ford that I need new rear discs and pads after only 13000 miles. Does this mean they were defective?

Depends on the reason why they need changing. Did they say?

You only need a stone or something get caught and it will score and wreck the disc and pad.

They said wear was down to 9mm and rusty in places. 

Probably only 'need' pads, but Ford will try to upsell discs as well.  Pads seem to be very soft on modern cars (not just Fords) so they don't last very long nowadays.

https://video.citnow.com/vtn6JbYvGn3

I stand corrected.  

Pads are fine.  Discs are wrecked - tiny pad contact area.  Sadly this is fairly normal for rear disc brakes.  As a driver, you need to brake hard every week or two to keep rear calipers in good condition.  I wouldn't say any of the parts were defective.

32 minutes ago, TomsFocus said:

Pads are fine.  Discs are wrecked

Yup !! that sums it up.

Is your car a manual ?

5 hours ago, TomsFocus said:

I stand corrected.  

Pads are fine.  Discs are wrecked - tiny pad contact area.  Sadly this is fairly normal for rear disc brakes.  As a driver, you need to brake hard every week or two to keep rear calipers in good condition.  I wouldn't say any of the parts were defective.

I get this on my MX%, alleviated by driving with the handbrake partly on evry now and again. Can't do this with the Ford however, 'cos the electric handbrake is either full on or fully off!

Yes, unfortunately not an unknown problem but I don't think any specific/exact reason for it has been found.

It was the same on Mk5 Mondeo when it was launched and prob seemed to go away.

Not just a Ford problem - have seen many posts on other forums such as Skoda and loads on the Jaguar forums