Scheduled maintenance will begin on PlayStation Network at 1pm British time. It will run until 2am tomorrow (16 October).
Throughout those 13 hours access to the store, transaction history, account registration and account management will be unavailable. Online play will still be available but you will have to log in (and stay logged in) before the maintenance begins.
Once maintenance has been completed your system will be all set for the re-launch of the PS Store this Wednesday (17 October).