Network Rail, which looks after the railway's tracks, signalling and power systems, has issued the following statement after this morning's engineering overrun:
"Passengers are being advised to check before they travel this morning on the main line from Brighton to London following a number of service alterations and knock-on delays.
"A broken-down engineering train has meant we have been unable to complete overnight work, leading to the closure of one of the four tracks in the Gatwick area. It has not been possible to repair the train, which has now been removed from site, and we are awaiting a replacement to complete the work.
"We know that this will be frustrating for passengers returning to work after the bank holiday and are very sorry for the delays they may experience while we work to restore a normal service on this route."