I've just heard (from a man on site) that the works currently being undertaken adjacent to the Up platform are to provide an alternative access to the platform. This will take about a month. Presumably this is to enable the booking hall to be closed for strengthening works. It shouldn't be a long term arrangement because TfL have said that when they are responsible for the station, the station will always be manned when trains are stopping at the station. I believe TfL take over the station in September in preparation for the arrival of the East London Railway trains from ?May next year.