There will be no services from Clapham Junction to Victoria, East Croydon or Gatwick Airport during the night.
For those passengers that still want to travel between Victoria, Clapham and Gatwick Airport at night, there will be the option of the National Express coach service. At night this costs from £8 single, takes 65 minutes, runs every hour and serves locations in South London, including Vauxhall, Streatham and Sutton.
I expect that by focusing overnight passenger services at the stations of St Pancras / Kings Cross and Blackfriars, which consistently achieve higher passenger satisfaction scores than Victoria, the rail industry can offer an improved passenger experience, including improved security.
There is a lot of work to do at both Victoria and Clapham Junction stations to bring the stations up to modern standards similar to Waterloo and London Bridge. A night time closure of both stations, albeit only for about four hours, will facilitate both minor and major work that needs to be done without the presence of passengers.