SeaFrance has ceased trading and no longer operates ferries between Dover and Calais
If you were thinking of booking then check out the alternatives:
P&O Ferries from Dover to Calais
DFDS
Ferry service from Dover to Calais
DFDS NorfolkLine from Dover to Dunkirk
Eurotunnel from Folkestone to Calais.
P&O Ferries and DFDS NorfolkLine are running extra services and have brought in extra ships. Information on these crossings and links to book can be found on the Drive-Alive ferries website. Please note that the DFDS service from Dover to Calais is operated jointly with LD Lines.