It's probably not any different in the UK, here there's a 1 year warranty on Tein components.
I'm running the full Super Street suspension system, massive improvement on stock, not had any functional issues at all, even on the shocking surfaces of some NZ roads. (Out of interest nothing mentioned here about not running the Super Street for road, in fact here it's one of the ones they recommend).
What sort of setting are you running your setup at???
Let me know if you need any pics of Zeds setup looks like, if that's any help.