Network Rail is facing a fine of £2 million after passengers suffered weeks of chaos on Thameslink and Southern services and delays at London Bridge.
Independent regulator, the Office of Rail and Road (ORR) made the decision after investigations into the company's Southern, Govia Thameslink services in 2014-15.
ORR found that Network Rail had breached its licence, with significant delays and cancellations to services.
However, the rail company has the opportunity to offer reparations for affected passengers, instead of having to pay the fine.
The severe winter storms took their toll on train punctuality last month, according to the latest official figures. A total of 87.1 per cent of trains ran on time in the period 2nd February to 1st March, compared with 91.1 per cent in the same period last year, Network Rail said.
Some train companies were able to maintain near-100 per cent punctuality records, but others were badly hit by the extreme weather which wrecked south and south west England services. Southern ran only 77.1 per cent of trains on time last month - well down on 88.5 per cent for February 2013.
First Great Western, affected by the severe damage to the coastal track at Dawlish in Devon, had a trains-on-time figure of only 80.4 per cent, compared with 91.8 per cent in February 2013.
Network Rail said Southern was affected last month by multiple landslips and flood sites.
Delays of up to 20 minutes on Southern between Worthing and Barnham, and between Worthing and Littlehampton due to signalling problem at Angmering. The signalling problem was caused by a lightning strike. There's currently no estimate for when normal service will resume.
Disruption on Southern between East Croydon and East Grinstead, and between East Croydon and Uckfield due to landslide between Woldingham and Oxted. Tickets being accepted on local buses, First Capital Connect and Southeastern services.
Trains can't run Woldingham-Oxted. Buses run East Grinstead -Three Bridges and Uckfield -Haywards Heath to connect with London trains. Trains run Oxted-East Grinstead half-hourly and Oxted-Uckfield hourly. Ongoing until at least Saturday 15th February.
Southern commuters will face a fare rise of 2.87% and Gatwick Express fares will be frozen at the 2013 prices.
The average fare rise will come into effect on 2nd January 2014.
Southern’s Commercial Director, Alex Foulds said: “There is good news for all of our season ticket holders as we have chosen not to use flex, meaning that all our season ticket holders will pay a lower increase.
"It’s also great news for our Gatwick Express passengers as we are freezing fares on the route, and for those looking for cheap off-peak travel, we continue to freeze our cheapest Advance fare at just £5.”
Delays of up to one hour on Southern between Brighton and Victoria, and between Littlehampton and Victoria due to signalling problem between Preston Park and Hassocks. Tickets being accepted on First Capital Connect and London Underground services.
There is disruption on Southern trains between Brighton and Victoria, between Brighton and Lewes, between Brighton and Southampton Central, between Brighton and Eastbourne and between Littlehampton and Victoria due to signalling problem at Preston Park.
Tickets being accepted on local bus routes. Severe disruption following a fire. A reduced service is running between Brighton and Three Bridges. Victoria-Littlehampton services diverted via Arundel. Hourly service and supplementary buses running Brighton-Lewes.
Replacement bus service running on Southern in both directions between Barnham and Horsham due to poor weather conditions at Christs Hospital. Tickets being accepted on South West Trains, First Capital Connect and First Great Western services.
Trains are now suspended with replacement buses running. Journey times may be extended by up to an hour and a half. Southern do not currently have an estimate for when a normal service will resume.