Mine has started to make this noise as well, mostly at biting point at very low revs in first gear and reverse. My local mechanic had a listen and said unless leaking or sound changes get louder he would leave it.
@[deleted] had the noise for about 3 years.
Not sure about Zaff but if it's like the astra it's either engine out or drop the subframe about 4 - 5 hrs work clutch release is about £110 for genuine or £70 for a decent branded item. Depending at the time might as well do the clutch at the same time.
After 3 people have looked at mine I am personally leaving it for the time been.
That's not yo say it could cause issues tomorrow or 1 mile down the road.
Sorry if this doesn't give you a direct answer.