The following can apply to vote by post in Greater London Authority elections by submitting an application to the Electoral Registration Officer (ERO) at their London borough:
a person aged 18 or over, who is registered to vote
a person aged 18 or over who has applied to be registered to vote
a person who has been appointed to vote as a proxy on behalf of someone else
The application must be received by the ERO by 5pm, 11 working days before the poll.1
The ERO has no discretion to extend the deadline for whatever reason.