Looks like root aphid - difficult to control, even chemically. suggest washing them off in a mix of insecticidal soap and water, cleaning them thoroughly to remove all traces of soil and bugs, then try repotting, not using the same pot without sterilising it in some way.

Can't tell you what the fungus is, but I have a friend who grows nothing but orchids and he never uses compost only special coconut husk to pot his orchids into.

Thanks both, I had thought of washing if off-I think the 'compost' is a bark medium which is how I bought it, and which is possibly similar to a coconut husk. I have a specialist orchid growing medium so I'll repot into that. Just hope its not too late as whatever it is on the roots seems very quick spreading.
I'll let you know how I get on.