The much-anticipated introduction of new train services between London and Kent has been further delayed.
Thameslink was initially due to begin linking Maidstone East with London Blackfriars and London St Pancras International from December 2018.
The launch was pushed back by 12 months, but the train firm and Network Rail have admitted that services cannot begin this year.
No revised start date has been given.
In a joint letter by Thameslink and Network Rail, the organisations said “a number of issues have been highlighted” since the commitment to introduce services in December 2019 was made.
Services could not be launched this year “without seriously compromising reliability”, the letter stated.
It was signed by Patrick Verwer, chief executive of Thameslink’s parent company Govia Thameslink Railway (GTR), and Network Rail route managing director John Halsall.
The pair acknowledged the “great deal of expectation surrounding the Maidstone East service” and accepted there will be “immense disappointment” by the further delay.
Tonbridge and Malling MP Tom Tugendhat described the announcement as “extremely disappointing”.
He added: “I am focused on working constructively with GTR and the Government to make sure any improvements are delivered next year.
“This will at the very least help long suffering commuters using the Maidstone East line during the key times of the day when people are travelling.
“There is no doubt that this is bad news, but I will continue to engage with GTR to ensure that they eventually do deliver what was promised.”
Rail timetables in Britain are changed twice a year, in May and December.
The May 2018 change crippled large parts of the network in the north and south-east of England.
Fears over a repeat have led to a scaling back of subsequent timetable changes, but this has delayed the launch of some new services.