Trains to Gatwick from London on Sunday 12 January will not run on Thameslink (St Pancras and stops via London Bridge).
Nor will the Gatwick Express run.
On Southern Railway trains will run every 30 minutes and be diverted taking 75 minutes from Victoria.
The alternative is to take a train from Victoria to East Grinstead (75 minute journey) then a rail replacement bus to Gatwick (25 minute journey). The bus will run every 5 minutes.