Passengers are being asked to only travel if necessary on the Southern, Great Northern and Thameslink network due to strike action.
Strike action on Saturday 1st and 8th October will mean there will be no service at all on many lines south of London, across London, or on the route to Ely and Kings Lynn.
Elsewhere, trains will start later and finish much earlier.
On Sunday 2nd October, services will start later and means only those travelling a short distance to the London Maraton will reach the start line on time.
GTR has released the following information:
Saturday 1st and 8th October
- Pre-planned engineering work will stop trains running between Brighton and Three Bridges as well as between Balham and West Croydon via Crystal Palace
- Around 18% of the timetable will operate, with crowding expected. GTR says this wil be made worse by ASLEF train drivers striking on other operators
- Trains wont start until 07:30am and will finish between 16:30 and 18:30.
- Gatwick Express will not operate – though the airport will be served by Southern and Thameslink with eight trains an hour in each direction.
Sunday 2nd and 9th October
- Services will start later
- Many trains wont arrive into Central London much earlier than 9am – only those travelling a short distance will make the London Marathon in time.
Wednesday 5th October
- Services extremely busy as ASLEF drivers strike on London Overground, LNER, Southeastern, East Midlands Railway and Greater Anglia.
- On the Tonbridge to Redhill route, a special timetable will be in place to support schools as this route is normally covered by Southeastern
Angie Doll, Chief Operating Officer, Govia Thameslink Railway, said: “It is with much regret that we have to advise our passengers to travel only if absolutely necessary on Saturdays 1 and 8 October. Strike action means train services across the country will be significantly limited, with many routes not running at all.
“Services will start much later in the morning. We expect our first trains to be very busy, so, if you can, please travel later in the day. Trains will also finish as early as 4.30pm, so plan ahead if you absolutely have to travel on these days.
“We're particularly concerned for London Marathon runners, who will have been training for this special event for many months, hoping to raise millions of pounds for charity, and the spectators.
“Our trains won't start that Sunday morning until around 7.30am and many won't reach central London until shortly before 9am. Only people making short journeys within London are likely to make the start line in time.
“We urge the unions to work with the industry and come to a resolution.”
That’s a Great Nothern unit, not a Thameslink. Or do they run both services?