"Merlin" wrote in message
I have two very productive quince trees, however a large proportion
of
the fruit is affected by a "problem". The skin has largish numbers
of
tiny black / grey dots and when you cut (hack!) the fruit open the
inside is heavily veined with brown to such an extent that 50%+ of
the
fruit mass is brown and because it's veined that makes 100% of the
fruit
mass useless.

I think it might be "quince fleck" aka quince black spot". Bordeaux
at bud burst.