I have searched the internet for a non chemical way to get rid of these pesky creatures. A mixture of vegetable oil and soap is all I can find.
Do any of you have another solution?
The RHS website suggests that while biological controls can be used to deal with aphids in greenhouses, there's no real alternative to chemical controls (other than squashing the aphids by hand) elsewhere:
http://www.rhs.org.uk/advice/profile?pid=181