A rail operator whose new timetable caused chaos across the country has been fined £5m by the regulator.
Hundreds of thousands of commuters faced delays for around eight weeks following the changes brought in by Govia Thameslink in May last year.
The Office of Rail and Road (ORR) said the operator, which runs Thameslink and Great Northern services, "failed to provide appropriate, accurate and timely information".
Some trains were permanently removed from the timetable but that was not made clear to passengers for several weeks, the regulator said.
At the peak of the problems, up to 470 Thameslink and 310 Great Northern trains were cancelled each day.
"The disruption experienced by many passengers as a result of the May timetable introduction was awful.
The ORR admitted providing "perfect advance information" for passengers was an impossible task for Govia Thameslink.
But it said "persistent and prolonger failures in information" led to a "severe lack of certainty up until the point of travel".
Staff were also poorly informed, leaving them with "little or no information" to help customers.
The ORR has written to all train companies and Network Rail to require them to review their crisis management plans and ensure appropriate arrangements exist for assisting passengers with disabilities in times of disruption.
Govia Thameslink (GTR) Chief Executive Patrick Verwer said he was "disappointed at today's fine" and insisted significant improvements had been made.
"These include upgrades to station screens, issuing frontline staff with new smartphones loaded with real-time service information, and we have volunteer teams on stand-by to help passengers during disruption.
GTR has paid £18m in compensation to customers and said it was investing a further £15m in improvements.