If you're not taking part in one of the country's largest sports events today, you might want to avoid central London – it's almost certain to be a travel nightmare.
But for those of you who are running/supporting/spectating, here are some top tips issued by Transport for London to help you get around the city.
All runners, race officials and on-duty St John Ambulance volunteers will be able to travel for free from early morning until 6:30pm on London Underground, London Buses, London Overground, DLR and Tram by showing their race number, officials’ course pass or tabard.
You have the good bit (at least when it comes to transport).
Southeastern is running extra trains to get people to the start lines in Greenwich, Maze Hill and Blackheath.
But there will be no trains to or from Charing Cross and Waterloo East to Greenwich and Maze Hill. You need to go via Cannon Street, stopping at London Bridge, to get to these start points.
TfL has advised that Cannon Street will be less busy so might be a better option on Sunday morning.
There are also no trains from London Bridge to Blackheath. To get to this blue start point, you need to go from Charing Cross, Waterloo East or Victoria.
Then you'll have no need for public transport for at least a couple more hours (lucky you) until you're at the other end of the 26.2 mile course.
Travel on Tube, Overground and DLR:
Spectators are being asked not to travel to the start line, which can get overcrowded.
According to TfL the easiest way to travel to and from the race will be by London Underground, Docklands Light Railway (DLR), bus or London Overground.
However they will also be very busy. TfL has warned that the Jubilee, District and Circle lines will be particularly crowded.
There will be changes to the routes and frequencies on DLR – TfL says to check before you travel and if you're travelling between Beckton and Tower Gateway or Woolwich Arsenal and Bank stations, passengers are advised to use the Jubilee line at Canning Town for services to and from central London.
Thinking about driving across central London on Sunday? Think again
Roads are going to be closed from 7am, and drivers are advised simply not even to bother. The road closures will run from Greenwick Park to St James' Park and will include all approaches to Upper Thames Street, Tower Hill and Victoria Embankment. Rotherhithe Tunnel, Tower Bridge, Southwark Bridge and Westminster Bridge will also be closed.
They will be re-opened in phases, and are expected to be fully re-opened by 7pm.
Buses travelling on roads affected by the Marathon will either be diverted or will not run the full length of their route until after the event.
Bus route diversions will apply from 6:30am-7pm, and will affect the following routes:
1, 3, 11, 12, 15, 15H, 24, 25, 29, 42, 47, 51, 53, 54, 78, 87, 88, 89, 91, 96, 99, 100, 108, 115, 122, 129, 132, 148, 159, 161, 177, 178, 180, 188, 199, 202, 211, 225, 244, 277, 286. 291, 341, 343, 344, 380, 381, 386, 422, 453, 469, 472, 486, C10, D3, D6, D7, D8, P12, RV1
London's Transport Commissioner, Sir Peter Hendy CBE – apparently without irony - said: “Public transport is the easiest way to get around on the day.
“I encourage anyone travelling around south east and central London to plan their journey in advance at tfl.gov.uk/marathon.”
TfL Travel Ambassadors, wearing magenta uniforms, will also be out on the day at Tube stations along the Virgin Money London Marathon route, providing travel information and assistance to customers.