Thanks for all the advice peeps.
We are treating with King British W 3 something or other - the price label took the name off
as advised by LFS - a good one I hasten to add.
We have culled one of the loaches sadly because he was absolutely COVERED in the stuff and looked completely miserable.
Still treating the other but if as is suggested it is because they are shoaling fish then that will only make matters worse. The only problem is of course, if it is the resistant strain of white spot then I don't want to introduce any more loaches in case then they get it. A bit of a catch 22 situation here!
Whatever the outcome I will keep you posted so if I finally cure them I will let you know.
Just as an add on - I bought the original loaches from an lfs I have not used before! Silly, silly me! When will I learn? Other fish incidentally appear to be fine.
Thanks again