We have, for some time now, been noticing small yellow spots appearing on
white washing. We recently bought a few new sets of white bed linen and
every single item has now been spotted with yellow marks.
This is becoming very frustrating as the marks cannot be removed.
We run a hot wash through our washing machine regularly and mostly wash at
30 degs, with the occasional 40 deg wash for some towels or bed linen.

Having googled this problem, it seems that it's quite common but no-one
seems to know the answer. Can anyone here enlighten me at all?

Jo