Anyone looking out of the window might have noticed that it's snowing - that snow has consequences. At time of writing National Rail Enquiries site is down due to overloading, and their phone number has similarly not responding under the strain. BBC Travel News is still running however, and a font of useful information.
Currently the entire bus network, the Hammersmith & City, Circle and Waterloo & City lines are suspended. The Bakerloo, Jubilee, Piccadilly, Northern and District lines are partly suspended.
London City and Heathrow airport are suspended as are the Heathrow and Gatwick Express train lines.