TfL website says:
"Major escalator refurbishment is taking place at Victoria Underground station until mid January 2012. Your journey will be easier if you can avoid entering the station between 1600 - 2000 on weekdays when: Queues are likely. There will be no ticketing facilities. A one-way system will be in place, including some entrances/exits. You may be asked to wait outside the station to prevent overcrowding. Once inside the station it may take up to 15 minutes to reach your platform. To avoid this disruption start your journey at nearby St. James's Park or Pimlico stations, which are easy to reach on foot or by local bus services from Victoria. For full details of how to avoid Victoria by using alternative Tube and bus routes in London and National Rail services to/from London visit www.tfl.gov.uk/vsu "
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"Victoria
Fewer delays, less congestion, step-free access and quicker journeys in and out of the station. Our work to improve Victoria station will improve journeys for millions of visitors and Londoners.
Your journey may be affected while we work on the station. It may be faster and easier to use an alternative route.
Improvements
A new underground North ticket hall at the junction of Bressenden Place and Victoria Street with an entrance at street level
Enlarging the existing Victoria line ticket hall (South ticket hall)
Nine new escalators
A new interchange tunnel connecting the two ticket halls
New lifts providing step-free access between street, ticket hall and Victoria line platform levels
New lifts providing interchange between the Victoria line and District and Circle lines platforms
Improved access and new lifts between the National Rail and Tube platforms
Timeline of works
Winter 2010
Completion of utilities diversions
Spring 2011
Construction of North ticket hall begins
Winter 2012
Extension of existing South ticket hall begins
Summer 2016
Opening of North ticket hall
Winter 2018
South ticket hall extension opens. All works complete
Note: These dates are indicative and may be subject to change."