A rail operator has had its worst period for punctuality in at least six years, new figures show.
In the four weeks to November 12, only 63.3% of Thameslink trains arrived within five minutes of their scheduled time, according to Network Rail data.
Press Association analysis found that this was the operator's poorest performance for any four-week period in publicly available records, which date back to April 2010.
Almost one in five (18.7%) Thameslink trains were cancelled or significantly late during the period.
This is also the worst performance recorded in published figures.
Thameslink, which is owned by Govia Thameslink Railway, the same franchise running Southern Railway, operates services between Bedford and Brighton through London.
A spokesman for Thameslink said its punctuality was affected by a number of incidents including major damage to overhead wires in Luton.
He said: "Quite simply, these figures reflect the catastrophic signal failure at Luton that cancelled all trains across central London and stopped most of our services north of St Pancras for the best part of three days.
"This and a track fire at Blackfriars, engineering overrun at West Hampstead, vandalism at Wivelsfield and the man who took off his shirt and jumped down on to the tracks at Norwood, delayed or cancelled a huge number of trains.
"We apologise, acknowledging that our passengers deserve better, and are working hard in-house and with Network Rail to improve performance."
On Tuesday a group of soccer fans endured a "rail journey from hell" on the Thameslink network after it took them more than five-and-a-half hours to get home from a game.
The Sutton United supporters were hit by a spate of cancellations after the Vanarama league game at Boreham Wood.
The match finished at 9.30pm and with the group of around 50 fans expecting a 90-minute journey home, they eventually arrived back in Sutton at 3.15am.
Thameslink apologised to the supporters and said the root of the problem was an empty test train becoming trapped at Herne Hill when the electrical supply to the track failed.
Rail, Maritime and Transport (RMT) union general secretary Mick Cash said: "Govia Thameslink Railway have become an international laughing stock and it is time for the Government to pull the plug on this continuing scandal that shames our transport network.
"They are in breach of contract and have been for months and they should be thrown off the tracks immediately and the publicly owned option, Directly Operated Railways, brought in to sort out the chaos GTR have unleashed."
Passengers on Southern services have suffered months of disruption caused by RMT strikes over changes to the role of conductors and high levels of staff sickness.