Tiny insect

I have no idea what this insect is but it is tiny- less than a centimetre.  I was  having breakfast when l noticed it crawling across a piece of paper towards me, l think it must have come off the glass of sweetpea flowers nearby.  I took the paper to the window and encouraged it to explore outdoors. 

Thanks to madwill backed up by Miranda, l now know it is an aphid!