Kent rail commuters have been warned they might face serious disruption to services to and from London for up to two years as a multi-million pound re-development of London Bridge station is carried out.
The warning has come from Southeastern boss Charles Horton, who said work at one of the country's busiest stations meant delays could be "significant" for thousands of rail passengers.
He compared the redevelopment to "open heart surgery", saying: "We have to get through this process to rebuild one of London's busiest rail arteries."
The first phase of redevelopment gets underway later this month, when three platforms are taken out of service as part of the £700m redevelopment.
However, this phase will affect only services run by Southern trains.
For Kent rail users, the critical period will be from the end of next year - when trains to Charing Cross would not stop at London Bridge.
Mr Horton said: "During certain periods of time, certain lines will not be available to operate trains. There are times when, if we do not get this right, the potential for services to be delayed is significant.
"It is our determination to do the very best to deliver as punctual and reliable services as we can."
He said platform rebuilding at London Bridge meant Charing Cross services would not call there until 2016.
Meanwhile, from 2016 to 2018, Cannon Street services would be unable to call at London Bridge.
Mr Horton was addressing the fifth annual Kent Rail Summit at Maidstone's County Hall.
In other comments that may not find favour with the county's rail users, he insisted Southeastern was now one of the most reliable train operators in the country.
"We are delivering some of the best punctuality and reliability figures that have ever been delivered on this part of the network.
"There are many opportunities to continue to improve services and deliver a better experience for passengers and that is our determination."