I've been using the hose to spray them off - you could use dilute washing up liquid in a spray, but I have noticed loads of ladybirds on the plants so as soon as their young hatch they will eat them.

Some people use a pressure washer with diluted soap or washing-up liquid - or a plastic glove to run your finger and thumb up the stem to 'squish' them if you're not too squeamish!

Snap, Cammomile! ;-)

Diluted Washing up liquid certainly does work well, but be careful to use a vegetable based one (such as Ecover) or you risk damaging the plant and/or the soil. Anti-bacterial soaps can be particularly hazardous to plants and soil micro-organisms alike

Predators work well too, particularly in enclosed spaces, plus the main bought-in Biological control species available for Aphids is a Ladybird, which is a completely natural and hardy British species.

There are a few other natural, easily & cheaply made-up plant-based sprays that might be worth trying out. There's an article on Ecocharlie with some spray "recipes" that you might find interesting:

http://www.ecocharlie.co.uk/blog/index.php/2010/03/08/plant-pests-%E2%80%93-ten-top-organic-solutions/

I've not tried Rhubarb spray but garlic & chilli definitely work well. We've used both on caterpillar & sawfly as well as aphids with excellent results....I guess they have a longer lasting, more residual effect than soap (which smothers the aphids) since they presumably make the foliage unpalatable but won't have any effect on edible crops like your beans. I do like the idea of using plants to defend other plants too!

Thank you very much these are very useful responses.