[wcndave]

I have two varieties growing here, mixed up, and this is spreading quite fast.

[AndyRVTR]

Looks like blight to me!

[wcndave]

Looks like blight to me!

And what to do about it?

[Hampshire Hog]

Not sure it matters which it is I’m afraid.
Only option I would say is remove affected plants ASAP.
That should reduce risk of spread and also allow more space for the unaffected plants.
Good luck HH

[steven c]

is the damage to leaves only in a small area we had similar that turned out to be a Fox marking its area, 

[AnneB]

We have had similar on our plot.  I wouldn't be pulling up your beans just yet. 

[wcndave]

is the damage to leaves only in a small area we had similar that turned out to be a Fox marking its area,

We live in the countryside, no foxes round here ;-)

I was thinking I would just remove the affected leave...