runner beans -black

Not sure what this was,was this the leaves or the bean pods.For this year just go ahead and see what happens as it is unlikley to be something soil bourne so you may just have been unlucky.

Anthracnose causes brown spots on bean pods.  Rotate the crop.

I think Anthracnose  is carried by the seed.  I'll go away and find out.

Bit of both by the sounds of it Aunty.

Google says "The fungal disease overwinters in and on seeds, soil and garden debris. Cool wet weather promotes its development, and the optimum temperature for continued growth of the spores is between 75-85 degrees F. Moisture is required for development and germination of the fungus as well as for infection of the plant. It is spread by wind, rain, insects, and garden tools.

Control: Choose resistant plant varieties when possible and use seeds which have not been exposed to the disease. If anthracnose is a common problem, do not save your own seed from plantings. To avoid spreading the disease, keep out of gardens when plants are wet and make sure to disinfect all garden tools (one part bleach to 4 parts water) after use. Do not compost infected leaves, fruit, or stems and thoroughly clean up garden areas in the fall, after harvest, to reduce over wintering sites for the fungal spores.
"

Mind you, we don't know that anthracnose was the actual problem ...

it was not brown spots more like covered in a black powder . Perhaps it was something that had been carried through the air. Not all of the beans were like this about 50/50