In Attack The Block our Protagonist, Moses, is the leader of a teenage 'gang.' In the opening of the film, we see two members of the gang on bikes. They cycle towards Sam before they mug her.
Cornish's decision to use the prop of the bike is arguably influenced by other successful science-fiction films.
I decided to research this further and found these interesting articles about bikes being used in film and their purpose:
We need to consider the purpose of this prop in Attack The Block:
Does Cornish use the bike as a 'symbol of childhood empowerment'?
Does he use them to represent 'the identities of the characters who ride them'?
Or is the prop just used as an emblem of youth?