Responding to Aslef's ballot result, Charles Horton, Govia Thameslink Railway's Chief Executive Officer, said:
"We believe this ballot was wholly unnecessary and unjustified in the first place and we're disappointed that the union is now contemplating industrial action.
"It’s perfectly safe for the driver to have sole responsibility for the operation of a modern train, and that's how a third of the trains up and down the country - with the full agreement and support of Aslef - already operate today.
"The travelling public has already suffered months of misery and hardship as a result of the RMT's pointless series of strikes. We urge Aslef to get round the table with us to continue our talks and resolve their dispute without causing further unnecessary grief to passengers."