Spray with soapy water or just hose them off.

Dilute soapy water is the way to go but make sure you thoroughly wash your beans before eating!

I have to agree that they would be mating, as it is the time of year, and we have so many ladybird larvare.

DO NOT TRY TO KILL BLACK & ORANGE CREATURES ON THE PLANT, AS THEY WILL BE THE LARVAE WHICH WILL HAPPILY MUNCH ON THE FLIES!

I've never found black fly on runner beans any problem, as the pest almost always disappears before the beans form and are harvested. If you spray with anything noxious you run the risk of killing off the predators which will automatically control the black fly.
It's a completely different story with broad beans, but I think you will find if you just leave them alone there will be no problem.

nip out the tops of the plants as that is where the blackfly first colonise

Mageth, I'd agree you do that on broad beans, and it's effective as the black fly don't seem to like the lower growth. But on runner beans, surely you'd be pinching out the growing point or leader. I know the plant would send out some secondary leaders but that would hold back the development of the beans. I still think the 'leave alone' approach or just spraying with a jet from a hose is the most effective way on runners.

oops Bertie, got me beans confused :o[