UPDATE: Sussex rail passengers are still facing significant delays and disruptions on the trains.
Several services from Brighton station were significantly delayed or cancelled this morning.
Many First Capital Connect Services are cancelled.
Commuters face further disruption as they try to make their way home this evening.
The cancellations are believed to have been caused by engineering work overrunning on the Brighton to Bedford route yesterday - rather than directly due to the adverse weather.
Passengers on Southern services have had to take bus replacement to Three Bridges.
Some passengers waited several hours this morning without a single train travelling to London.
One commuter said it had taken her more than an hourt and a half to travel from Hassocks to Brighton.
First Capital Connect are saying on their website: "Owing to snow earlier between Bedford and Brighton fewer trains are able to run on all lines.
"Train services running through these stations may be cancelled, delayed by up to 60 mins or revised at short notice. Disruption is expected until 2am on Tuesday.
"We strongly advise customers to allow additional time for their journeys and to check departure boards for their station at www.firstcapitalconnect.co.uk regularly for the latest available information on train times."
FCC staff at the station said that the problem was partially due to trains having been left in Gatwick last night.
Brighton station staff said further problems were being caused by train drivers being stuck at other destinations so unable to man the trains they were supposed to be driving.
- Southern services currently cancelled between Brighton and Hove
- Southern services currently cancelled between Lewes and Brighton
- 14.25 Southern service from Brighton to London Victoria cancelled due to weather.
- FCC services from Bedford to Brighton running approximately half an hour late
- Londn Victoria to Brighton services running on revised timetable - those trains that are running are about 20 minutes behind schedule.
Are you having problems with the trains? Call The Argus newsroom on 01273 544.
The icy weather has already had an impact on the county's public transport this morning.
Southern has reported trains are not running between Lewes and Haywards Heath due to "the late finish of improvement works, which has delayed our lines being treated to remove the build up of ice".
Buses are operating between Haywards Heath and Lewes instead.
Passengers travelling towards London from West Coast stations can travel via the Arun Valley line between Barnham and Three Bridges.
Passengers from East Coast stations can travel via Eastbourne and Hastings and then via South Eastern Trains services via Tonbridge to London Bridge and Charing Cross stations.
There are also problems between Horsham and Dorking with buses operating on the route instead.
London Buses, London Tramlink and London Underground are accepting Southern ticket holders by any reasonable route.
Southern has advised it will be operating an amended timetable but this timetable will be subject to alteration with some cancellations.
We will bring you the latest disruptions as and when we get them.
Southeastern is also being affected by the ice.
A spokesman said: "We running our regular timetable, however the snow and ice of the last few days is causing delays and disrupted services on some routes.
"Several trains this morning will be cancelled. Where possible we'll run longer trains with more carriages to reduce the chance of them failing.
"Please check before leaving home see if your service is still running and if you're travelling allow additional time for your journey."
And First Capital Connect have reported the Bedford to Brighton line is "severely disrupted".
Passengers are advised to check their trains here and allow extra time for journeys.
Brighton and Hove bus company is running an almost full service this morning.
Services 23 and 25 are unable to reach either university campus, so are terminating at Falmer Station.
In Steyning the 2A is operating a ONE WAY LOOP via the by-pass, Horsham Road, the High Street, where the buses will terminate, then continuing via Clays Hill and normal route back to Shoreham and Brighton.
Service 20/20X is operating normally except not serving Shootingfield (terminating at the High Street/Grammar School).
Service 22 is running normally, except not via Langley Crescent.
Services 23 and 25 are unable to reach either campus, so are terminating at Falmer Station.
Service 27 is operating between Dyke Road Avenue/A27 roundabout and Saltdean Coombe Vale. Buses are still unable to operate through to Westdene but we can operate normally in Saltdean.
Services 28 and 29 are operating normally, except unable to serve Whitehill, Steel Cross or Tunbridge Wells Sainsburys (buses operating direct via the A26 in all instances).
Service 46 is operating full route normally, except not via Rotherfield Crescent and Cuckmere Way in Hollingbury (buses will terminate/re-start at Asda).
Gatwick Airport is running as normal but passengers can expect some delays to flights due to weather conditions across the UK and Europe.