The main train operator for Brighton and Hove has highlighted two more days of engineering works requiring passengers to travel on replacement buses.
Southern said that the work was taking place on the main line between Redhill and East Croydon on Sunday (10 January) and again on Sunday 31 January.
The company said: “There will be no Gatwick Express service and revised Thameslink and Southern services on both days.
“Travel by train between London and Gatwick and London and the coast will still be possible, but journeys will be diverted, will take longer and trains may be busier.
“Replacement bus services will also be in place to help passengers complete their journeys.
“Passengers travelling from Brighton to London Victoria will be able to take the train to Three Bridges for a connecting bus to East Grinstead where the journey can be completed by train.
“This journey will take between 2 and 2½ hours.”
In general passengers are being advised to allow at least an extra hour for journeys between Brighton and Hove and London.
Southern added: “Travelling by train from Brighton or coastal stations to Gatwick Airport is unaffected.”