Spray with a systemic insecticide - that way you'll only have to do it every 2 weeks. I know lots of people recommend soapy water, etc., but you'd need to do that at least once a day to keep them at bay.

They have killed all the flowers and the plants are just wilting now, can they be saved or do I have to cut them right back, thankyou for your reply

Unlikely to be aphid attack that's killed the whole plant - are they wilting through lack of water? Remove any dead flowerheads and stalks, and dead leaves.

Lupins are also loved by slugs,